Valve spring seat difference?

Regarding: In the 73 transition between 750 and 850...
What is the difference between the 06.1399 (850) and the 06.7545 (750), ? Is it the I.D. for the 850 which had the Cir-clipped valve guides and not the stepped shoulder?
The kibblewhite bronze guides for the 850 have the stepped sholder.
Was there a thickness difference and was all 4 heat washers used? I think the Combats didn't use the heat washers on the intake IIRC due to the 2S cam?
The combats were 06.7474
Thanks in advance.
Tom

850 has a 5/8" guide vs the 750s 1/2" guide. The spring seat for the 850 has a larger hole for the guide. Also check whether the guide you are using needs to use the circlip or not, the guides i got from RGM were grooved for the clip, but did not need it and the fit was much better without them.

thanks, Maasey