Way too many variables, suspension? Crossmembers? Sticky Tires or Skinny Bias plaies? it all depends on those! Tim Gangle had 500+ HP through one in that sedan he raced on the first season of Pinks, and that was a model A Fram i believe...
All depends on how you build it ,With a real x member like I build them It would .Even though my frame is a 32 ,Ill have no flexing issues,Granted Im only gonna run 300 to 325 horses.Check out my thread Ive been framed ,Havent added to it in awhile,Ive been working to much,And not on car
built my A in 65-66 boxed and heavy duty cross member no roll bar till last few years drag&street raced HARD....5.38 gears&slicks only problem rivits came loose on rear xmember.......
Kindred spirits................ Boxing, front end, welding, rear end set up. You have been "here" so long. I love learning from the "ones" who know.
You can box the frame all you want to but if you don't have good cross members welded in , then it will still twist . You have to have all for corners tight with strong cross members in the middle to keep the twist out . Honestly by the time you go through all that work with an old frame , why not just build a NEW good box frame instead ? That would be the best way to go . Just my opinion . Retro Jim