yamaha 2.6l cylinder heads - what's the difference?

[Tinkertoy250]

doing a stock rebuild of a 1989 225hp Excel and the 6k7/6R5 heads are long discontinued. there seem to be a lot of different heads that all use the same head gasket, water jacket covers etc. 6k7, 6r5, 6g5, 6g4, 64e etc. i have a new set of 64e heads. the only difference i can see is the threaded hole for the thermosensor is too small for my sensor, but i easily drilled and tapped it to fit. people on forums seem to say there is a difference and some are better than others. i have a corroded 6k7 and 6r5 as well as the new 64e. used some straight edges and caliper to measure distance from the head surface into the combustion chamber at various points and they seem identical in every way. all the water passages are the same also., am i missing something? should the 64e heads work fine on my excel? i called around to a few used outboard shops looking for 6k7 and they all said the 2.6 heads are interchangeable.

[88workcar]

They are interchangeable. Just use the set that has the smallest chambers.

[Tinkertoy250]

They are interchangeable. Just use the set that has the smallest chambers.

thanks. I’m going with the 64E since I already have them new