as above run what you have and build as you can afford a better motor. if you can't find a reasonably priced 360 in your area to add a 4" stroker kit to (for 408") then a cheap 318 with the same 4" stroke doesn't give up much at 390". add ally heads of your choice/budget along with cam, inlet, headers and dual exhaust.
those last 2 could be added to the 318 for now so you at least have the 'sound' if not a great hp jump. they'll work better with the bigger motor later.
neil.
ps if you opt for stroking a 318 be ready for all the 'tiny bore' and 'valve shrouding' comments when in reality it's only 90 thou (45 thou all round) smaller than the 360 that they will also tell you you must have, lol.
neil.
valve shrouding'comments/haters when in reality it's only 90 thou smaller than a 360.