David, I think the early style UZ fires pairs of injectors for its version of batch fire? If so, that means you'll need to find 4 spare wires in your harness to setup the injectors for sequential. That or you'll need to talk to Doc Tweak...
As I'm sure you know, with sequential injection, each injector gets an individual output from the new ECU, instead of pairs of injectors getting an output. They'll all still share a common +12v "rail" from the master relay.
Going standalone is a big step. You'll get some big advantages with tuning, but probably some disadvantages with driveability, interoperability with the OEM equipment, etc. Maybe you could look at letting a new ECU handle only the injection, and keep the OEM to handle the rest?
If the problem with the batch fired injectors is simply an impedance mismatch, AEM makes a low impedance, peak & hold driver box that could help with that.