manual to auto, pickup to burb, 3/4 to 1/2 ton, tranny question!

[speesh]

Hi there,
I have a 71 Burb 1/2 ton that I drive daily, and it now has a 3 speed manual tranny. I want to change it to an automatic, and I happen to have a long wheelbase '69 3/4 ton pickup sitting around with a rebuilt Turbo 400 tranny in it. What would it take to change this over? I know I need a radiator, tranny cooler lines,flywheel, starter, crossmember, and shifter (all of these can come from the '69, right?). My big question is about the driveshaft: actually 2 questions.
A: will the driveshaft from the ' 69 longbed pickup be the right length for a suburban?
B: what about the rear u-joint? are they the same from a 1/2 ton to a 3/4 ton? I doubt it, and if not, what do I do about it?

I tried using search but couldn't really figure out how to ask it what I was searching for!

or should I go for a 700R4? I would like better mileage, but I already have 3.08 rear gears, would a 700R4 still be an improvement? I hear they are not as reliable and I already have the TH400........ I already get about 15 mpg on the highway, is that pretty good and will it go down if I do this changeover?


Dang, I ask a lot of questions!

[Bowtie67]

Depending on the lengths of your current trans and the TH400 you may be able to just change the trans yoke. The stearing column, radiator, crossmember should all change over, your original start should be same, as far as flywheels go, if they are both SBC chevy engines Not the 400SBC you should be all set here as well. The biggest concern here is the lengths of the drive shaft and I think you should be fine here as well.