Justin,
Most of the reproduction parts vendors sell a torque-tube rear end 3.55 ratio conversion gear set. A strongly recommended separate purchase is an installation kit. That installation kit includes all the gaskets, seals, bushings, and bewaring for a rear-end "rebuild".
If you are going to use your 3.90 ring and pinion and it looks worn/pitted, contact me (my email is in my profile).
You will need a Shop Manual for disassembly and re-assembly instructions. You will also need a dial gauge and stand to adjust the lash and gear bluing (Prussian Blue) to adjust the gear-tooth contact (pattern).
At some times you will need another person - it makes the job safer and quicker.
Good luck,
Tim
Jim Carter HP166 Patrick\'s ring & pinion installation kit
