why could early 360s run with 250 plus HP stock?

or you could mill your heads down to 49cc with the mopar thin gaskets and have 10:1 with stock pistons. Of course you have to get the intake fitted and then there is the valve to piston clearance that might be a problem if you run a big cam. Custom fit pushrods......and on and on.That's what happened to me when I took my heads in to be milled and didn't specify a minimum cc to the builder. He just did what I said and milled the heads .050.
Seems to run fairly good in my 63 dart with 3.23 and 904. Haven't been to a track or anything yet but, I hope to soon. When I build my next 360 it will definately be zero decked and correct pistons to improve the quench area and flow.