What's the compression height for a 360 magnum as buying pistons

Ah OK, I used the wrong combustion chamber volume; your numbers are no doubt right. I now get 8.32 with .050" thick head gaskets.

How much boost are you planning? And will this be ECU controlled fuel injection or carbed?

No reason you cannot grind out some cc's from the chambers, and maybe use tulip-headed valves, all the get more volume. I've ground out 8 cc's from chambers before to set SCR with the desired pistons. (But not SBM's so I can't advise on where the thin spots may be).