I am installing the lt1 in an 88 IROC. Do I need to find a 91/92 cluster for the speedometer and tachometer to interface. I will have to use an adaptor on the T5 for the vss and can run the cable also from there, but does the tach get input from the PCM meaning I will need a different tach? Plans are to install a t56 later and then the adaptor for the speedometer cable will be gone, but I need the t5 for now.

 

The LT1 PCM has to get a signal from a VSS for it to run correctly, then you can run the output signal to a conversion box and run a cable to the speedo. The tach is just a tach output, no changes needed there. To be honest, I would wait until you can get the T56 before doing the swap, the conversion boxes are around 300-400 bucks and could be money to put toward a 6-speed.