New 66 Dart owner

Welcome aboard, and congrats on your purchase. Don't forget that these 66 and older A Bodies are narrower in the engine compartment that the 67 and later models. You CAN put a big block in there, but you'll run into a whole bunch of little problems, the biggest of which will be exhaust manifolds/headers. On the other hand, any of the LA small blocks drop right in there with a minimum of headaches, especially if it's an original 273 car. The 66 uses the same K Member for both the slant 6 and the V8's, so you just need engine mounts, a suitable matching tranny, and either manifolds or headers to complete the simple swap. Good luck.