If the head is stamped with an RH number above the right exhaust rocker cover, the numbers RH4 (32 mm intake port) or RH10 (30 mm intake port), it is a normal 850 head. There was also an RH9 850 head with 32 mm intake ports and higher compression ratio, but you almost never see one. RH7 and RH8 heads were 850 head bolt pattern and bore size, but were for the short stroke 750 and had full hemi chambers with no squish band. and larger intake valves. You're unlikely to run across one of them very often. Any other RH numbers make it a 750 head of one sort or another. If it has no RH number stamped (and that's fairly common), you can either measure the diameter of the counterbore, as LAB suggested, or look at the head bolt pattern. If you're going to swap meets looking for heads, a simple solution is to just take an old 850 head gaskset along and use it to check the bolt patterns. The differences are really obvious using a gasket, but maybe not so obvious just looking at the head.
For comparison, this is a 750 cylinder head
And this is an 850 head
You can see the difference in space between head bolt holes and the combustion chamber counterbore, as well as the wider squish area in the 850 head, but it's not such a huge difference if you're just looking over heads at the swap meet.
You can ignore the other differences, like valve size and the bronze seat. The 750 is an Axtell ported head, and the 850 is a Maney stage 2 head, so there have been some mods. I didn't have any pictures of stock heads to use.
Ken
