Yeah considering it had the 700r4, the only control the computer would be looking to achieve would be the TCC. And yep, in his case, the VSS is located in the transfer case, so nothing wrong there. But there will be idle RPM differences, and also spark advance differences in the PROM. Not enough of a difference that it's life or death or anything like that, but I personally had to make these changes in my auto prom when I went from auto to manual to get it to run smooth.'89 had a 4L60, not a 4L60E, so the only care the computer has about the transmission is an output to the torque converter clutch. AFAIK it doesn't even take a reading from the VSS. If it's programmed any differently, I don't think it will endanger your ECM, transmission, nor engine.