In terms of circuitry they are almost the same.
The mic amp is a neat little discrete transistor class-A design that sounds very good… it’s streets better than the later IC mic amps that everyone now uses (except myself and a couple of other designers). And don’t forget, these mixers were built to a very exacting spec. and had to pass both the IBA Code of Practice, and the BBC spec for on-air continuity mixers.
I have had a look and I don’t have circuits for these mixers. 😥