It goes without say, but the first thing I would be doing is testing the ECU in a working Aristo (i know that'll be tricky if you don't know anyone) Eliminating the ECU itself being faulty is a pretty logical first step. I can't see why it wouldn't run if you have a factory ECU in the conversion running fine. FYI, I swapped a Mines ECU into my 2J'd MZ20 Soarer with no issues.
It is however common for these ECUs to start having issues with leaking capacitors and what not. So yeah, I'd try testing it in another car first.
2nd logical thing to check is that all the pins are in good condition, i.e. no bent or snapped ones