What about a bone yard 360 Magnum with TBI? Or a 383 and TBI? The Magnum 360 heads are a lot better from what I here than earlier LA heads. The 383 would allow you to pick a middle size combo if you want a lot more torque. You can offset grind a 383 crank to 3.54 or close, put a set of BBC rods in it with custom pistons so you can use a more modern ring pack(less drag) and have a range of 388 to 420 cubes so the mileage is decent. The 383 based engine would have mostly shelf stock parts in case you ever need to go through it again. Same with the magnum, and you would have a hydraulic roller cam as well. The Magnum would offer a better valve train stock. Not having added up costs for the various combos, I would think the 360 Magnum ought to offer the best combo at a fairly low cost.