Here is a rabbit hole for your consideration! The PDP-8 had an optional card set called the EAE for Extended Arithmetic Element. These cards performed asynchronous math calculations as described in the attached screenshot. Better yet, the coding manual and circuit diagrams are available online here:

http://vandermark.ch/pdp8/index.php?n=H ... Arithmetic

http://vandermark.ch/pdp8/uploads/Hardw ... awings.pdf

On the circuit diagrams I see some standard TTL glue logic, counters, multiplexers and some ROMs. I attached a photo of the boards from the links. The circuit diagrams are especially interesting. If you have any other links I'd enjoy seeing them. Thanks!

Just in case someone follows this link while doing a search... here is a detailed explanation of how the EAE works, as posted by a helpful member over at the Vintage Computer Forum.

http://vandermark.ch/pdp8/uploads/Emula ... AE-ocr.pdf

The PDP 8/a had floating point hardware option as well, to give full hardware floating point in the mid 70's.