The video roms are not the problem, I swapped them and both SE's still show the same problems.

Swapping the roms was one of the things I've tried, I found out that sometimes, the roms in a ceramic package loose their content. (I've spent ages troubleshooting an IBM XT Clone only to find this out...)

UE8 is a new part, it is a SN74LS166AD from TI, I bought it here