F-250 axle/susp. swap

I have an '88 F-250 4x2 supercab that is in excellent condition with really low miles on her,and I'd like to convert her into a 4x4 in which to pull a boat around as well as plowing snow. My dilema is I don't know in what span/range of years I should be looking into for a donor vehicle whereas the leaf springs,axles and other components won't require major surgery.Any suggestions will be greatly appreciated.  Thanks,Boskey IV