Can anyone tell me if there are any other valve springs that will easily inter-change with a 235/261 Chevy?

Most any cam company can provide you with something that will work. But first, you have to know some pertinent info or you risk camshaft or lifter failure.

1) valve lift
2) hydraulic or solid lift cam
3) valve spring installed height
4) valve spring OD

These are the big questions they will ask you first, they also could ask additional questions regarding you cylinder head, like valve stem size(if retainers are also needed), etc... so be prepared to give detailed info to them. Without knowing this information, they cannot provide you with the best spring for your needs.

I used Buick 455 valve springs on a 261,good for about .475 travel. These are a single spring with a flat inner damper.The spring fit fine on the head seat, a bit tight on the stock spring retainer. Used a set of inexpensive aftermarket retainers intended for oversize springs on Chevy V-8. The springs installed height was Buick spec,a bit more length than the stock spring.Required no shims.The Buick springs are about 10 percent stiffer.

I guess that I should have been a little more specific. It is a solid lifter '56 235. I am trying to do a low budget refresh on an engine that has an aftermarket 264 degree cam and solid lifters in it but the previous owner wanted to keep the head to put on a 261 build. I was hoping that there might be some more common (cheaper) dual valve springs that might fit with a minimum of machine work.

The 455 springs might be a good answer Tony P. Thanks

I guess that I should have been a little more specific. It is a solid lifter '56 235. I am trying to do a low budget refresh on an engine that has an aftermarket 264 degree cam and solid lifters in it but the previous owner wanted to keep the head to put on a 261 build. I was hoping that there might be some more common (cheaper) dual valve springs that might fit with a minimum of machine work.

The 455 springs might be a good answer Tony P. Thanks

You will need to know what the installed height is of the valves to be able to correctly determine what valve spring you will need. A solid lift cam requires more spring pressure than a hydraulic cam of the same lift, so its not simply a matter of just slapping them on there and go, its more involved than that. You will have to find a valve spring that will provide the 1)correct closed spring pressure at the valves installed height, 2)while allowing enough total travel for the valve without being too close to coil bind or having the retainer hit the valve guide or seal, and still provide the 3)correct open spring pressure, while also 4)fitting the spring pocket for the cylinder head. Once you find a spring that will meet all 4 of these requirements, thats the spring you will need. Installing a spring that is too weak or too strong can cause serious engine damage and failure, this is a place you should never consider taking a shortcut.

The Buick 455 springs have an installed height of 1.9 and coil bind at about .510 lift.The stock 235 springs have an installed height of 1.85 and coil bind occurs at about .440.The coil bind comes off actual measurements on a properly done 235 #848 head on my recent 261 build.I used a solid lifter cam reground cam with an actual .430 lift.Any 235-261 street cam will be less than an actual .440 lift when figuring in valve lash. And actual lift taken from a mocked up engine.
The Buick springs are about 3 bucks each,
Or you can just call a major cam grinder as mentioned above.

TRW shows 2 different 455 BBB springs, both single coil with damper. I suspect the VS1020 is for the Grand Sport.
VS1016 is 295 lbs. per inch of deflection (a little less than stock), VS1020 is 373 lbs. per inch and will give high open pressure if you're not careful.
The reason there are not more interchanges is that the stovebolt springs are an odd OD, about 1.35". The more common 1.25" springs will work but you can't use the original collars.

Awhile back I thumbed through the Comp Cams catalog and found that the 961 springs had almost identical specs to the original 235s and the 910 springs were similial to what a 261 would've used.

Here's the specs I used for comparison: http://www.canadianmilitarypattern.com/1960%20235-261%20Engine%20Manual.htm and http://www.compcams.com/Base/pdf/ValveSpringChart.pdf

Many head castings seat the spring in a machined recess which limits the spring OD. I'm not sure if the size and depth changed over time, but the shape of the recess itself has - measure yours, and use a spring as close a fit as you can find.
It may be safe to enlarge the recess OD, but there's water under there; don't be the first to find out.

This is great stuff guys!

I don't have the exact figures here...But...On a spring testing machine the 455 Buick spring was about 10 pounds more at closed pressure and 20 pounds more at .430 lift than a new stock spring.About 240 pounds actual.I spent a bit of time at the machine shop testing springs.The problem is I don't remember the part number.
The primary reason I used the Buick springs was to avoid coil bind of the stock springs.
If coil bind isn't an issue I believe with the non aggressive cams grinds used on street 235-261's,that stock springs will be ok up to about 4500 rpm.

Predicting how a spring will behave is pretty simple if the specs are known.
The spring rate (not always given) is in pounds per inch of deflection: how much weight squishes it exactly 1"?
To calculate this from know pressure (like valve closed and valve open to a given lift):
Subtract the closed (lower) pressure from the open pressure, like 208 - 82 = 126 lbs.
Now divide it by the lift, like .396 (the stock 261 lift), and get 318 lbs. per inch. This is how you predict a pressure change with different assembled heights and/or lifts.
Example: adding .100" to the lift increases only the open pressure by 318 (the rate) by .100" (the change) = 31.8 lbs. becomes 240 lbs.
Increasing the assembled height by .050" = 15.9 lbs., so the new pressures are 66 lbs. and 192 lbs.

Generally, a faster-opening cam requires more open pressure - but higher lift generates higher open pressure automatically as above.
Higher engine speed needs somewhat higher closed pressure to stop the valve from bouncing as it closes.