I have swapped modern engine in an old car(71 510 w/ 97 KA24DE) and replaced factory ecu with an AEM standalone ecu but didn't tune it. All the wiring is new so far I have not had any issues
I know about some of the RFI issues and importance of good grounds. When I was a tech 30 years ago
we had fun chasing down gremlins caused by bad grounds. My car has the a modern alt and Firecore wires but the wiring is mostly original. I was interested in the Terminator Stealth for the ability to upgrade to “HP” ECU specs with a free online software download and keeping the ecu out of the engine bay for reliability. Not sure it is worth 2x cost to me. I would like to learn how to setup fuel and spark tables.