Big intake valves

[3W Hank]

I just read it is possible to use a 1.72” intake valves and 1.6” exhaust.
I thought 1.6” on both was max.
My 41 Merc blick is rather ported but I’ll seen bigger and its still has the 1.5” valves.
I can’t see on my block how a ring that wide can has a material under in the runner ?
Here is a picture on 1.72-1.60.