My brother just gave me a 91 F250 4x4 with a blown motor. The only things worth salvaging on the truck are the axles and transmission. Can I use the axles and suspension on my 86 F150?

 

No, they will not fit. You could put your f150 body on that frame. That would be a bolt-on deal if it's the same wheelbase. But then you need a engine. Don't know what you have in each truck to see if they are swappable.

 

What would I have to do to make them fit?

 

Use the f250 frame. The f250 front axle is made for leaf springs, your f150 has coils. The f250 front axles are shorter, so you would have to custom mount the pivot brackets for the frontend. What a mess. Nothing will bolt up and work except maybe the rearend. And in the end you have the f250 running gear on the lighter f150 frame.