Mystery solved....its an H74 round port head extensively modified from standard.
Has some corrosion on the head, is this anything to be concerned about?

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Bronze valve guides will not last like stock chilled cast iron nissan ones so look at wear in that area and replace with stock nissan if worn out, If as new then use till worn out and go from there

Well I’ve bought it so the mystery will be solved once its shipped.....

Looks like a H75 with work done to it
porting, chamber work and welded water galleries
I doubt its an a12 with that much work done to it
just to end up with a semi open chamber
H75 slightly shaved gives that

Just looking at the pics on Tech wiki... could be my eyes playing tricks on me and this pic is dirty compared to some clean pics so who knows...

I don't see any clear difference there. Do you have a photo of a round-ish one?

Thanks for the follow up. It makes sense it's a round port head with port work to make them oval shaped. One other question, all the A12 head pics appear to have rounded edges etc where as this head appears to have straighter edges? Don't know if that makes any difference to the type of head it could be.

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It seems that only Round-port heads have those shapes

this is the only one with Hump-shape on intake face. But then we don't have photos of every head type ... The 728 may be similar but no photo
G25 from B120 1979-1989

It seems that only Round-port heads have those shapes

this is the only one with Hump-shape on intake face. But then we don't have photos of every head type ... The 728 may be similar but no photo
G25 from B120 1979-1989

I was looking at the photos of heads with/out water holes below the intake ports. And with "hump" shape of casting instead of "triangle" shape

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