So, i was just looking into that old and beaten Classic i had in a box for what seems like years. Caps are leaked, green muck on the traces, it still starts, but without sound. The hardware is pretty much the usual, memory expansion to 4 MB and a hard disk.

And i found this:



The daughterboard is connected with that white thing at the top. Which looks like that from the side, only three traced connections really:



This is the top view, sorry for the bad picture:



The chip has nothing on it, except this sticker:



The bottom view has an empty socket. I would say that a FPU could fit:



It says:

MODAM MAC CLASSIC ADAPTOR

© 1990 MEMORY PLUS

and:

PH X1B-S03

The white connector board is, at least i believe it is, just a power connection, not a data connection. This should be the data connection, 8 pins, but nothing was connected: