My sister just bought an 89 f350 drw 7.3 idi with 1st Gen Banks and c6. She currently has 4.10 rear end. She wants the 3.73s for better fuel economy and she just graduated high school so she won't be doing much towing if any but has her nose up at the 3.55s I have. I would love to know what junkyard vehicle would have the ring and pinion I need and what driven gear (end of speedometer cable) I would need so that the speedometer on the dash is still correct. Any help would be appreciated.