I had a 54 with a mild built 350 back in the mid 80's and early 90's and never had a frame problem, my cousin still has the car. The 41 that I have now has A 383 tuned port with a mild cam and over 25000 miles with no problems.
How much hp, and how are you going to use the car, ie drag racing or street. There are several streetrod vendors that build new frames for that vintage Chevy. I do know of some that have used 78 to 88 Gm A body, Monte Carlo Malibu frames under 49 to 54 Chevys, but I think they have to be lengthened to work.