I drilled the crank on my '60 261 (same for 235) not difficult at all, picked up a bolt & washer kit for a V8 small block. Once you have hole drilled and tapped get it started by using a piece of 4x4 wood and drive her on with your BFH, should go on pretty easy, make sure mating surfaces are without burrs etc. Can pull the balancer home with your new bolt and once it's in place coat the threads with anti seize.

It's easier to get forgiveness than permission!
1946 1/2-Ton Chevy
1953 Chevy 3/4-ton Factory Stakebed