Question about rear end change and trans leak

[bwilder10h]

I just bought an 85 shortbed that an older guy owned and plan to do some rust repair/paint/wheels and eventually a new engine and have the 700R4 rebuilt.

The first week I had it, I put a new oil pan gasket on it and also the trans pan was dripping and the rear seal on the trans was leaking. Well, that bad news is it was dry on my garage floor for a couple days and now trans fluid is dripping out of the hole in the converter cover. Is it safe to assume the only thing I didn't replace is a front seal that requires the trans to be removed from the back of the engine block?


I was also noticing on the factory tag in the glovebox that shows options on the truck from GM that the rear end is a 2.73...
I didn't know they put such a weak gear in these trucks. Anyway, I want to at least take it to a 3.55 or 3.73 and would like to get posi. Right now it's open (dont ask me how I know...) and a posi would be nice for after I drop a new engine in it and replace the weak 305 which doesn't run bad, just not enough. The trans is all over the place now shifting in and out of overdrive and it's ridiculous. Also wouldn't mind knowing what 12 bolt rear ends fit it... as in what vehicles to look at in the junkyard to find a complete rear end, rather than having the gear changed and still being a single tire smoker...

Thanks for all the help. I attached a pic of what the truck looks like now. Not bad for 23 years old. Interior is perfect....