Don't know what motor to swap in.

long time ago in a land faraway...well, I had bought a Dart that had a stock 68 440 installed, 727 with 340 convertor, 3.23 SG 8-3/4. engine had 1-5/8" Hedman (?) headers. ran good, lots of torque. took out 440/727 installed 68 340/4-speed with day 2 pieces (LD-340,3310,1-3/4 headers,electronic ignition,484/284 MP cam). small block combo was a lot more fun and easier to haul around corners. too much weight on the nose with BB. choice obviously is yours alone, but that is my experience. Good luck with your project, either way you go.