yeah with an 700r4 your wiring will be a bit different. the speedo miscal is because the VSS reluctor ring in the T56 is ALOT different than the automatics, for mine I had to recalibrate the PCM for the correct output. I'm not overly familiar with the TBI controls, but you might need to get a conversion box of some sort (like a dakota digital or something.) I'll try to look around and see what I can find out about them but I'm not too well versed on the OBDI signal processes...I THINK the VSS on an 89 just runs directly up to the gauge?
the reverse lights should be pretty simple to fix, the reverse light connector on the T56 is just a simple open/closed switch, so you can find the reverse lights wire on your truck, then splice into that line so that the switch on the T56 is providing power when reverse is activated....I hope that makes sense, I'm just headed out right now, and I'll try to clarify when I get home if needed