Critique/suggestions on 273 engine build

318 would be my choice - your heads will work with some larger valves (1.88/1.60's), and they are already closed chamber, if they are truly 66's. You can also reuse the crank - most 273's had forged cranks which can be balanced easily for a 318 or 340 for that matter. 273 pistons used an insanely heavy walled wrist pin to make up the bob weight for the crank, I suspect the original cranks were used in semi hemi 318's which would explain the insane wrist pins.

I'd pull it apart and see what you have and then reuse a bunch of the internals inside a late model 318 engine. If you get a hyd roller motor block then your cam options become even more interesting. Consider putting a hot rod roller hyd cam in it. They make tons of torque if chosen correctly. You can reuse the intake and carb as well - so you've got alot of the pieces already sitting inside or on the 273. What you'd need is a set of pistons and rods and a good core block, and valve train parts. Go grab a 318 from a late 80's dippy or truck and do it to it. If you use some stock off the shelf pistons you can get close to 9 or 9.5 to one using thin head gaskets. You can easily meet the 300 hp level with a modest cam and some well chosen parts. Plus a 318 looks exactly the same as a 273, no changes to engine mounts or anything, and if automatic or manual for that matter it will bolt directly to it with no other changes either.