Alrighty then. This should be very doable for you. A great many parts especially external accesories are shared between the entire sv family from 266 thru 392. If you're not looking to swap the transmission over also, this will be even easier. Based on that assumption, what you'll need to do once you have both engines separated from their trannys, is remove the automatic trans ring gear known as a flexplate from the back of the 345. You'll also need to remove the mounting hub. The starter for auto-equipped rigs has a spacer shim on it for proper starter drive gear and flexplate meshing. You'll need to remove this and re-install the starter without the shim for the manual trans application. Then do basically the same on the 304 engine. Transfer the flywheel, hub and bolts from the dead 304 onto the 345. Compare the oil pans on both engines. If they differ, you will need to swap over the pan, pump, and pickup from the 304 as to avoid any clearance issues. How about the exhaust manifolds? You May need to swap those over too if the 345 has rear dump and the '66 requires center dump. Motor mounts? Those May be different between the two as well. Swap 'em over if need be. The primary items that aren't swappable between the two engines include the intake manifold, (& possibly the carb, this depends on how both engines are currently equipped), valley pan, cylinder heads and pushrods. That list May be incomplete, but those are all that come to mind immediately. Hope that helps. Good luck with it.
