I agree with everyone else on it lasting depending on your driving habits. But, how many miles and what condition are ther rear and 700R4 currently in? If you never put sticky tires on the car and don't try to do Hooper style launches at every stoplight - the stock rear should hold up fairly well. When you do gears and a posi I assume you will do all new bearings.

Even on street tires that spin, your 700R4 will most likely be toast from the added torque. Invest in good parts, and a trans cooler. SFC's are a very good mod, I did then even when I had the stock LB9.

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1986 IROC-Z, 8pt. cage, 383, Mini Ram, DFI, Art Carr 700R4, 12 bolt.....

 

The stock tranny and rear are pushing 105,000 miles