Duece,the typical 261 head gasket has a compressed thickness of about .055,Detroit gasket used to have one that was .042 compressed.
Using a 848 head,milling the block and head .030 each,will give a 261 around 9-1 actual compression with flat top pistons set no more than .010 below the block deck.You may have detonation with higher compression depending on cam grind.
All the stock style oversize replacement pistons I've seen place the piston down the bore .030-.040 at TDC.Do a mock up with the pistons in the bore before milling the block.Do pay attention to the piston to valve clearance on the intakes if milling the head and using a hi performance cam.I never had a interference problem,but some supposedly do.
