I saw my favourite words.
"Schematics are available"

https://tumbleweed.nu/lm-3/schematics.html

LM-3 --- MIT CADR schematics

So somehow I've ended up on a bit of a rabbit hole.

Schematics for the MIT CADR LISP machine are available, and in fact there's already an FPGA implementation!

https://tumbleweed.nu/r/uhdl/doc/trunk/README.md

uhdl: Documentation

That said the target FPGAs are a bit... Unusual.

Either a pipistrello board (a xilinx Spartan 6) or an Arty S7 (Artix-7).

Maybe something that could be ported to a Tang FPGA?

@DosFox The Gowin FPGAs are the exotic ones. Spartan-6 and Artix-7 are so much middle-of-the-road, it couldn't get more common.
You can't imagine how widespread Xilinx FPGAs are in the industry.