I have a 700r4 behind a 350 (both from an 88 c1500). Eventually I want to create a full feature instrument cluster with gauges that glow red. For now, I'll use the stock base model cluster that came with the 78, but the speedo is mechanical and the sender is electronic. I have a th350 that from could borrow the tailpeice from.
Is it that simple? Just undo the four bolts on the tail and swap? Eventually I want to but an electronic speedo in but I still have yet to turn her over and drive her.

 

I don't believe they are the same length or diameter where the the O-ring meets the case....I could be wrong. you will also have to see if there is a difference in drive vs. driven gear location since that housing did not come on that trans. Honestly, that housing is cheap though you can probobly get one and be assured its all good.

 

You will have to remove the tailstock housing from the 700R4 and on the tailshaft is a reluctor type wheel that is pressed on to the shaft and exchange it with the correct speedo gear and press the gear onto the shaft I beleive the housings are the same (correct me if I am wrong) then you will require the proper speedo drive that matches the gear