How different are the 172/182 heads to the 197/200? Would it be possible to machine/port the 182 to flow as well and be as effiecient as the 197/200 would be if that were ported etc, or are they quite different in design?
Good question there mate! The combustion chamber is a different design, but you could replicate it on the 1*2 head. It's a relatively simple machining job, but obviously they all need to have the same volume.
To get the ports the same - your fucked. That's the simple truth. The exhaust ports are pretty much identical position wise, but they're slightly smaller on the 197, although that's no real drama. The 200 maybe the same but I've not seen one. I'd imagine they are tbh. Inlet port entries are higher up than the 1*2 head so you'd have to weld up the inlets to put back the material that's been removed to create the original 1*2 port. Then once the heat from the welding has distorted/warped the head you start wondering why you bothered. Lol!
I adapted a 197 inlet to fit on to a 172 ph2 cylinder head a few years back, so that's how I know the ins and outs. It's a huge task to do the job and it's simply not worth the grief. I didn't do the welding up of the ports, it's what I found out after I'd adapted the head/inlet.