Can someone please answer these questions for me ....
1.I am replacing my trans from a 84 Z28,700non electronic with a 87 rebuilt 700 electronic.can i do this and how?Am i screwed cause of the different modulators?I have one wire on the trans in the car and the 87 has a three prong hook-up,what do i need to make it work good?
thanks.

 

700R4's weren't electronic in 87, the 4L60E is the electronic version and it wasn't out until 93. The 87 transmission will connect up just like your 84.

 

These trannies don't have 'modulators'...

For the speedo gears, just swap out the original sender by removing the retainer and ripping it out (be gentle with a twisting pulling motion... it's only plastic)

Now to be dead on accurate with the speedo, when you have the sender (driven) gear out, shine a flashlight in there and note the color of the plastic gear inside. If it's not the same as your original transmission, remove the tailshaft (4 bolts) on both you old one and the new one and swap them. Simply press down on the metal clip while tapping it off.