The p8R head has VTEC sized valves, and the ports are as big as a VTEC head.

The combustion chamber is 84mm, but i dont think that matters because:
1) There are guys running Stock VTEC heads on 84.5mm blocks with 84.5mm Headgaskets. I dont see them blowing headdgaskets all the time.

2) I believe the headgasket would seal fine 84mm with a 81mm headgasket.

Let me think about this one an run some numbers aka talk to Don.

The cams are not that different, an i wouldnt classify them as an upgrade anymore than the 01 ITR Intake cam vs the 98 ITR intake cam (3 deg difference)

P8R should be 33mm Intake valve and 28mm Exhaust Valve, same as any VTEC head.