I wish I knew more about this but I needed some help. I am in the process of buying a 1969 Mach 1 Fastback with a 351 Windsor. It currently has an automatic transmission with overdrive (I was told). I do not know the type yet. (have not taken delivery of the car). I will eventually switch it out for a standard 5 or 6 speed Tremec.

For now though I had a question. The rearend is a posi-traction. I was wanting to know what kind of rearend gear (3.73/3.90/etc.) I need to get a decent cruising car for both street and highway?

Any advice would help. Also where can I buy the gears to have them put in the rearend? It's a Ford 9" from what I remember.

Thanks very much,

 

determine for sure what rear gears you have now and custom order matching gears for your trans .. no sense buying both .. my car has 4;10 gears and a five speed with 31 inch tall tires .. perfect for me ..