swap out the slant 6

Great point and advice.

Heres a thought....Low mileage Magnum 360 engine with these parts swapped out/added.

single plane intake from MoPar
750 cfm carb
Big tube headers
Create engine cam and springs
Add LA water pump and timing cover with fuel pump ecentric and fuel pump for carb.

Now, you just did a copy of the 360/380 HP create engine for cheap. Just make sure the engine is a low mileage unit.