We've been working on this project for a little bit now. Mostly iterating through pen and paper designs and descriptions to figure out what we even want to build, up to the first iteration of the schematic from earlier this week. The design is heavily based on Usagi Electric's UETTL, though I have added some features, made substitutions (CMOS mono and astables instead of 555s, 74HC251s instead of 74HC4051s and so on) and most of the clock and control logic is taken from my earlier Uno TTL computer project.

The front panel design and interface concept is largely sorted, as is preliminary component and footprint selection. I was able to track down some super stylish and cheap paddle switches from Unicorn Electronics (they still have an eBay store!), so I'll be working those in the design.

Obviously these plus the vintage RAMs with separate ins and outs make the build tricky to replicate, so I may work some modifications into version 2. For now parts are available enough through NOS sellers.