Calling all 318 guys....318 vs 5.2 magnum, info needed please

I dont need necesseraly to stay with 3.23....i know i ask a lo but my last 2x 340s and las 360la were miserable in traffic and overheated like crazy all the time no matter what....im thinking since in my area ( montreal , canada ) the 5.9s are getting rare and expensive and forget the 340 blocks...i saw on internet some 1989-90 318s and 5.2s for like 150$...5.9s they go for 600-900$ more..i did everything i could for the body of the cuda , its all done , bought the 4 speed....but can afford a high dollar engine....and like i said i just want a small block that can equals or beat the 340 in power and mpg and be reliable and that the parts can be bought everywere , i can afford a 3-4-5k engine right now , just want to make the car move by its own power. So 5.9 is the only to go ? I had an offer today for a 1971 318la with 30 over pistons.....but im looking for 300+ hp .....trow out your ideas guys , if the only small block bang for the buck is the 5.9 then ill go with it , but i was thinking about the cheap and smaller 5.2.....underdog !