did the 1991 F250s come with 12 bolt rears and 1o bolt up front ??

 

91 F-250 has a sterling 10.25 rear axle. if it is a four wheel drive, it could have either a Dana 44 IFS, or a Dana 50 IFS front axle.

 

Yes it is 4wd I belive it it has be swaped or just had the cover changed b/c it has a old rusted chrome pumpkin cover and it seems to be a lot bigger then other 250s I've seen

 

Neither.. that's GM terminology and thankfully we don't have to deal with any of that junk on these trucks. A GM 10bolt is equivalent to a Ford 7.5" which was used on the little 1/4 ton Ranger while the 12 bolt was roughly the same as the 8.8" or 9" found in 1/2 ton Ford trucks. The axle in your F250 is bigger again with a 10.25" ring gear and if your truck is over 8500lb GVWR then it has the full floater 10.25 with a Dana 50 TTB front axle.

 

Thanks very help full My truck is rated at 8800 if I remember however still leaves the question ... If the guy that had The truck before me swaped gears I can't imagine anybody just putting the chrome cover over that pumpkin without doing anything else Thoughts? Would you agree?

 

seeing a chrome or aluminum cover on a rear doesn't indicate there's been a gear change.to find that out,there are many ways (google) such as checking the rpm to speed and comparing it to an online drive train calc.
some people find 10.50 covers in the salve yards/online that come on the late model SD trucks for improved cooling and bolt those on their 10.25's for example.this doesn't mean they swapped gears too.

post up a pic.we'll check it out with ya.