So i am doing an engine & tranny swap and my 85 elky. It came with a 4.3w/smog pump & 200r tranny. I have placed a 91 silvarado 5.7 engine, 700r4 tranny and computer in the elky. I am unable to hook the tranny up since the elky has a speedo cable and the tranny is elctronic. Also i am leaving off the smog pump since it is of age now and is not required to pass inspection. Will i have to remove the existing wiring harness and place the silvarado's or a newer one in? I so lost right now that I need a step by step book on how to line everything up and get the right parts. Please give me your comments on how to tie everything together and back on the road since I need all the help I can get, Thanks

There is a speedometer gear that can be added on the th700r4 tailshaft for your speedometer---the electronic one will probably break when you pull it off unless you use heat, which I don't recom mend if its already in the car---just pull it and let it break. the one for the speedometer is a clipon and is held in place with a lock spring. As for the engine If they are both TBI injection then the computer should be fine so minimum wiring change....I swapped a 350 into an old 89 pickup that had a 4.3 and it worked just fine....I'm not sure the 91 engine is the same injector systwm as the 87 so you may need to swap the actual injector unit over to the v8 so it will work with the computer you have.............dan

Thanks, for the input! I think I am getting to the point to just go get a 400 tranny since the El Camino could have this option and should work, but I will not get as good gas milage if I do this. i was really wanting to make this 700r4 work. Oh what to do? Didn't chevy make a 700r4 that had the speedo cable connection?

Yes it is a GM part, the transmissions came both ways---mechanical speedometer and electronic speedometer---its a simple little slip on gear on the output shaft for the mechanical speedo the electronic one is a multitooth magnetic reluctor thats pressed on, I've changed them both ways to get what I needed at the time.
The transmissions changed over from a hydraulic control valvebody to an electronic shift after 93 and it became a 4L60E the only electronic control on the earlier transmissions is a lockup solenoid for the torque converter.........Dan

You have to remove the tail shaft housing of course, to get to the output shaft to change to gear etc. Not a big job, and a good time to replace the bushing and seal in the tail shaft housing.
1995 was the last year for the CCC computer system.