What flywheel can I use for my 261 at Bonneville? I assume the stock piece is cast iron, right?

Correct. Try locating an aluminum flywheel.Won't be easy though.

I thought one of the guys on the HAMB was making his own (one off) for his HA/GR car with a used slipper clutch floater as the friction surface.

I forget who, or which thread, shoot, it may have been Ron G, or maybe not.

Not sure on a 261 but a GMC you can make the center hole on a BBC the correct size then drill 6 new holes to match the crankshaft and it will work.
At Bonneville you will need either a steel or non-cast aluminum. What ever you find I would add 3 5/16" or 3/8" dowels...(36 years on the salt with inlines).
Check with Clifford Research...Not cheap but what is now days.....Good Luck

Check with SCTA to see if they need SFI certification etc before spending any money.

In the past as a SCTA inspector, when I got to the line on the inspection about the flywheel of a manual shift vehicle I would ask what the material the flywheel was constructed from and write it down on the form. ei: steel or non cast aluminum. I never asked a competitor to prove it's origin or whether it met SFI specs. I don't know if anyone ever did. My current flywheel is made by Ron Hamel at 10,000 RPM but it has no tag and never did. The one I bought from Gary Hart is a converted BBC and it doesn't have one either. The ones I had made for me by McLeod didn't either.

As competitor we all buy many SFI meeting parts from supply houses ie dampers, flywheels, flexplates, etc for use on street and race cars but the SCTA in it's wisdom has not needed proof and dates for these parts as the NHRA demands. I'm one who is glad they don't. They have dates for safety which don't follow the NHRA either. Can you inagine buying a $1500 fire suit every 5 years when you may wear it once a year?.

Concern over Cast Iron flywheels is obvious. None of use wants to see one fly apart that's why they are prohibited. If you "lied" about it's material and it came apart I'm sure you would be asked to leave and not allowed to come back.

It seems this is being asked because manufactures don't make them for typically economic reasons. I've never paid under $400 for a GMC and am glad to have them. Every one has been made because I can supply a stock cast iron to copy. (I always get it back). This may the way you will need to go.........Good Luck

Thanks for the help from all of you. The search for parts continues!

davenm, let me check with a buddy who just had one custom made for his V8 combo in a drag car.I'll see if I can get some info for you as to who did his.

Here's the website for Rob Porters' Advanced Clutches;
http://www.advancedclutches.com/

Thanks a bunch for the tip on Advanced Clutches. I'll contact them.