Just a hint.. What about using am2901 instead of 74181?

[Roman Pollak]

Really impressing! But instead using 74181 as an option, I suggest am2901. All you need is in it. 8 registers (dual port ram), alu, shift etc. Browse old amd stuff on bitsavers.org

Rgds
Roman

[jdh]

Thanks for the suggestion, would probably consider it with a redesign :-)