Rods and crank in that order. The 235 rods are really only good to 4800rpm although I have had them as high as 6000 rpm (one time and I was young, still have the motor, lol). Small end is the big problem. The 261 truck rod is slightly stronger. Small end is still a problem. You can do a 302 gmc rod, and they are good to at least 6000 rpm, if not more, but be forewarned they are heavy and it’s a lot of work, I have them in my 261 motor. The big end of the rod has to be machined/narrowed down to 235/261 size, small end bushed, .990 floating pins, big block rod bolts modified to fit. The 302 rods are slightly longer then the 235/261 rods so You will need custom pistons with the correct compression distance measured out. 302 Rod bearings have to be narrowed a bit to fit the 235/261 crank. Cam has to be clearanced in between the lobes to clear the rod bolts. The rub, you either have to order the cam with the clearances machined (and you will have to sort out how much needs to be removed ahead of time). If you try to do it after you have the cam ground, you run the risk of nicking the cam no matter how many precautions you take (I did it and had to send the cam back to Schneider for a regrind) and the clearancing actually screws up the cam (twists and bends) and yes, discovered that when I sent it back because I had nicked it. Lots of work. Yes, there is a thread of my build, I think it’s “chamfering rod Bearings” or something similar. I have a couple of hundred miles on the motor, and probably 15 runs down the strip at the trifive nationals and the combo runs pretty well but only time will tell as to longevity.
This is my son driving the car (my actual high school car from the 70s, took my drivers test in it when I was 16 in 77) down the Beach Bend Dragstrip this past August. He was driving the car for the first time.https://www.youtube.com/watch?v=lMVz66tyrKQ
As for the crank, it is a cast steel crank but it’s old, heavy and long. You can grind/polish all the casting marks, index and equalize the throws, balance it, drill the snout for a balancer bolt, and even use the BHJ balancer (I did not have the money at the time I was finishing up my motor so I am using the stock balancer) but it does not change the nature of the part. I broke a 235 crank a good many years ago at a drag strip and I can tell you it’s no fun, messed up the entire motor.
My current motor gets to 5000 rpm in a flash, and at the strip (which is not all that often) I will shift at 5500 but that is really as high as I want to buzz the motor, mostly because the harmonics start to come into play at higher rpms (If not at 5000 rpm. Tom Langdon sticks to his guns on this number suggesting that anything over 5000 rpm runs the risk of vibrations, harmonics, loose flywheel bolts, etc.)and because the head stops breathing before 5500 rpm, probably around 5000 or maybe even a speck lower, and I have big valves, relieved chambers, polished, and removed the land that locates the retaining ring for the intake manifold. You can actually feel the motor run out of flow. With a head less modified, the motor ran out of air earlier. That is not an issue for you but the pressure on the crank and rods should be.
There is also the 292 rod caddy piston stroker conversion but that is also a good bit of work and I have no idea whether that conversion will withstand the pressure given the way the offset ground crank is what holds the rods in place (unless you go to the expense and trouble of welding up the cheeks of the crank to provide a proper side to side crank clearance. I have not done that build and do not think I will because of the overbore on a 261 block necessary to do the conversion and I simply don't trust that the machined crank will hold the rod from side to side.