I don't believe converting to the earlier higher mounted water pump will cure overheating problems of a cracked head.
Get another head first before you drill and modify your block.
Fixing cracks on cast iron blocks or heads is really difficult and few welders can do that job right and reliable nowadays.
I'm a 'fan' (hoho) of the later style water pumps.
The later water pumps have the impeller actually right inside the block and are distributing the coolant inside the block more efficiently than the earlier type with the impeller outside of the block with only two small holes accessing the block. The earlier pumps have a smaller diameter pulley than the later ones, so they spin faster because of their inefficient impeller design, but this also invites cavitation at higher rpm.
I would always stay with the matching stock water pump to your block, just like the engineers designed it for good reason.
To center the later pump more towards the radiator, you can drill extra holes on the radiator mounts that are an inch lower and drop the radiator, which will also allow for longer more efficient fan blades, like the light efficient aluminum or stainless flex-a-lite (low profile) fans. That's an easier, more effective and cheaper upgrade than the adapter plate, in my opinion.
You get six blades and a lot more pulling power through the radiator at slow speed than the original fans.
The walker shroud will be great for slow driving, like in a parade.
Also good for lower rpm and speed city driving.
Not so good for high speed freeway driving though, when you want a clutch fan or no fan and shroud ideally.
