1964 Dart GT - Bought it because my wife likes it.

You can get the spacer from Pat "Torqueflite Patty" Blais, tflitepatty@verizon.net . Probably easier to drop the trans to install it, but that depends on what tools, space, and facilities you have available to you.

Y'don't necessarily have to swap in a V8 to have fun, and you don't have to waste money with the clowns at Clifford to get hot rod parts for slant-6s; there are lots of other, better options. See for example Dutra Duals and header options discussed in this thread and this one, Erson custom cams, HEI ignition upgrade, Mike Jeffreys windage trays, Hurricane intakes, other exotic intakes. Hi-perf engine buildup here, high-perf parts and build info here.