65 Barracuda tranny

The good news is, you don't have to swap the K member. 273 brackets and insulators will bolt in a 273 or 318. If you want a 340 or 360 you will need conversion mounts (Schumacher comes to mind) and the aforementioned center link. Don't forget the 90 degree oil filter adapter and 273 exhaust manifolds or very pricey headers.
Now, for the hard part. Prior to 1966 Ma Mopar used a ball and trunnion driveline instead of the later slip yoke and U joint setup. You can pick up a V8 ball and trunnion transmission which will let you keep your current shifter, drive shaft, and rear end; or you can swap to the later slip yoke tranny, drive shaft, and rear end. If you go this route, plan on buying a shifter. You may also need to find a 64-66 cable throttle pedal assembly if you have the rod linkage on your slant. Hope this helps.