Easiest/Cheapest way to a 4bbl 318?

I would still go with a set of magnum heads over 302's, the bigger port and valve size will allow the engine to breath way better, I like your idea of getting a $130 U-pull it 5.9 magnum and building a stroker motor with a set of INDY X heads, then you could use the stock magnum heads on your 318 with a cam while you build the stroker (just make sure the lifters you get are oil through the pushrod type), the swap is very straight forward and if the heads came off of a running motor they should be fine, and it would be more economical to use the same magnum style air gap or crosswind intake on both motors, I see summit doesnt have the conversion pushrods but they shouldnt be hard to find, and new valve springs are always a good idea when installing a bigger than stock cam

http://www.dippy.org/forum2/index.php/topic,295.0.html

http://www.moparmusclemagazine.com/techarticles/mopp_0409_318_engine_build/index.html