Why do you people quote stroganoff340... I have to glance over that crap and he's on ignore...
For the OP. If you must use a 318 block, just put a 4" arm in it and move on. Easiest way to get your power goal with a reasonable, very streetable camshft. You can put a bunch more duration in a 4" stroker engine and not have the ill effects of poor idle/vacuum quality like in a smaller engine.
And stroganoff340's car is still missing 2-3 MPH with his 416 if it's really making 520-530hp and he has NO IDEA what a properly built 360 runs like... 11.70's... you're kidding right... so take anything he says with a grain of salt. 8)
Carry on with the fun.