Driveshaft change questions

[Joshpow]

I am planning on putting a 78 c4 in my truck. It has a slip yoke and long tail shaft. I got a bolt on and short shaft. My driveshaft has the slide in it. My question is how to figure the length to have my driveshaft cut after I change the transmission. The guy is giving me a long bed driveshaft to cut with the transmission. I just need to know how to cut it the right length. I am afraid of getting it too long or short. Anyone know how to measure for the driveshaft? With the truck on level sitting on the wheels or rear wheels raised?

Also, is there a chance that a swb 3 spd manual would be right. I got one of those in my 71 if it would be the right length.

Thanks Guys.

[fordman]

you would do it similar to i described befor but you need to figure out the slip yokelngth to the u joint that holds the slip joint. i am not sure i can explain what i was told. but i will try. the old slip joint shaft will have a wear spot on it from being in the transmission. measure fromt he spot on the slip joint itself to the center of that first ujoint. then measure from the rear seal of the trans to the rear end yoke center. with some addition or subtraction you should get your length.

[willowbilly3]

You will need to install the transmission and then take the measurement. You really can't guess how long a shaft you need before you are ready for it.

[Joshpow]

I understand willowbilly. I just wondered if anyone had done the same swap to have an idea. Anyone know how to measure the length when the transmission is in? I am assuming it would be with the yoke midways between all the way in and all the way out. Any ideas?