3K for a junk yard engine & trans with a few bolt on parts would be OK. The engine mounts can be obtained from Schumacher creative services. They have the spool style mounts. The biscuits are sandwich looking. The spool is round at the bottom.
After the engine trans package deal, the engine mods are easy picks.
Carb, cam, intake, headers, distributor. An electric fuel pump (Edelbrock makes a low psi unit for carbs, ez wire in.) for the Magnum engines or convert the the older set up from the timing cover forward. Also a cam nose extension from Hughesengines. To work with a Magnum cam. A switch to a LA cam is better IMO. Be careful of the lift!
Worry about heads last. You can closely copy the MoPar 360/380 hp engine with a Comp cam that is very close to the MP cam. These engines use the stock head (with the cams correctly matching valve springs) and normally produce over 400 hp. The rpm intake will add excellent torque and give back nothing on the big end.