Yes; a three carb setup will fit/work on a 49-54 auto. It's way to much carburation for a stock 235" engine though.
Yes; you can bore +.125" on those which gives you 252 CID.
Your 'best bet' for the money is to find a 261" engine & go (+.125) with it. You would then have 278 CID to work with etc.
Good luck.
