273
The 273 will cost you more to build, but your car looks pretty original and nice. If you want to keep it pretty much stock, get that 273 block and fix it. If you want to get a 318 block, all of your existing rotating assembly except the pistons will work right back into a 318 block, and you could use off the shelf pistons such as KB167's. Get it balanced with your existing flywheel and it all bolts right back in. I just built a 273 for my 65 Barracuda. I bought custom pistons from Race Tek and they were $700 per set.....since I bought 3 sets! I got 2 sets for me and another set for another FABO member. I built the one for the 65 just to say I'd done one and have to do 1 more because it's the numbers matching engine for our 69 Dart GT convertible. If I were you I would avoid a 360 because it will force you to buy a special 130 tooth flywheel, a 10.5" bell housing and special made linkage to make your clutch work. Decisions, decisions! :BangHead: Good luck with it.
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