What engine for my dart?

There is no diff between a 340 an 360 motor mounts. The 273 and 318 mounts are different, but you can still space 'em...if you don't have the factory ones. Droppin in a small block is still a SB. A 360 may have a bit more grunt at the bottom, but a 340 will rev faster and higher...Never did like the 400 (unless you change the heads,cam, ect) Sounds like you built a Stroker..Heck Yeah!!!!!