Ive got access to basically complete 91 f250 diesel with 1 ton axles. I mainly just need the rear axle only.  what kind of axle did ford use on this year of truck and what are the pros and cons? should i grab it while i can?  

I believe it's a Dana 50 front Twin Traction Beam.  You don't want this axle because it is Ford's earliest form of Independent front suspension.  There are many cons to this axle in build ups and I would not mess around with it.  Depending on how large of tires you plan to go with, I'd recommend 2 different options.  If 35's or smaller, a straight Dana 44, which is a very plentiful axle and should be easy to find.  If you are going with a larger tire, then you should try and find a straight Dana 60 off either an F-350 or a pre '79 F-250.   

It could have been a 10.25 sterling or a D70 in the rear of it. Up front that can with a D50 TTB as stated above which is basically nothing more than a D44 with a slightly heavier housing and axles but same ring and pinion.

thanks for the input on the f250 axle. by the size of the pumpkin(huge) i'll assume its a Dana 70.  what are there strengths and weaknesses? Ive got what i believe to be a 31 spline, 3/4 ton, corp 14 bolt on my sideyard that i was going to do an overhaul on until i found the f250. how does the d70 compare to the corp 14?  

The D70 and the 14 bolt 10.5 are nearly equal with edge being given to the D70. It is anot a big difference though.