Milling the earlier head enough to get the compression increase of the 848 will result in the intake valves hitting the pistons unless the valves are recessed into the head the same amount it's milled. That shrouds the valves and reduces volumetric efficiency. Just find an 848 head, get it reworked, and bolt it on.
Jerry
Do you remember the thread not to long ago where a member had engine work done and a valve was hitting the piston. That was a good read. I believe you posted on it. Jeffrey
