A lot will depend on how much you want to keep stock, and how much you're willing to change......and your budget for doing it. If you want to keep it stock, get the correct '65 273 4bbl intake and a carb to match. That will be a bolt-on and no mods needed. If you want to go with the later small block stuff, the sky's the limit. Keep the valve size down (use only 273 and 318 heads and not the big port 340/360 versions) and don't overcam it. Later large chamber heads would need higher compression pistons to keep the ratio and power up. Later close chambered heads will need some mods, both for plugging unneeded holes and, as mentioned by Commando66, some grinding on the driver's side to get clearance for the stock exhaust manifold. The exhaust manifold ports will match up with any of the small block, small port, cylinder heads.
