In the end, for what you want, the 273 would be the best in my opinion. There are a lot of different parts and adjustments to be made with any other engines, if all you need is a cam and crankshaft (273 or 318). Head gaskets are nothing, been using small block ( 273, 318, 340, 360) Fel-Pro .040 head gaskets since the 70's. Everything else being the same. Fix the trans and the small 7 1/4 rear should be fine with the 273. Every engine has plus and minus points. A 273 has closed chamber heads, 8.8:1 compression, bushed rods, and a solid cam valvetrain. Use the original exhaust manifolds, they will work with 273, 318 or magnum ports. A 273 in good condition will have plenty of power in an 65 Barracuda. I ran a 273 from mild to wild for 20+ years and 250,000 miles. You can always upgrade later down the road. All that being said, take some time and see what is available.
