318 Build? Help!

Bummer... I'd be leaning towards a 5.2/5.9 Magnum swap in that case though. 5.9L Magnum with a reground cam, 4-bbl intake+carb and headers would make well over 300 HP and it is very possible to find high-mileage Magnums that don't require a rebuild. Stock 5.9L flex plate has external balance weights so you can keep your current torque converter. Or stick with 318/5.2L displacement which are cheaper and more plentiful and internally balanced.

FWIW I put a 5.9L Magnum short block with LA top end in place of a 360 LA in my Duster and it was very straightforward, hardly had to change anything.