[mnunn454]

I have a 3.55/TH700 in my 3900lb 454 70 El Camino with 275/50/15s in the rear. It's the perfect ratio as far as I'm concerned. Highway RPMs at 60 are about 2200. At 70, they're about 2400.

3.42's or 3.73s are as close as you can get with the truck carrier to a car 3.55 12-bolt. 3.73's will work on your current (4.11) carrier. 3.42's require a different carrier (which is no biggie if you're buying a posi anyway).

Powertrax makes a unit that replaces the spider and axle gears in your current carrier. I've heard they're fairly easy to install and don't require you set up the R&P all over again. Pros and Cons on both sides of this approach.

I have a 3.73 posi in my 69 C-10 with TH400/454. It spins too fast for me on the highway. I have a spare TH700 that one day I may rebuild and install in it.

I'd think 3.73/TH700 and your 350 engine would be a really sweet combo.

A cheaper alternative to your current delimma may be to just run rear tires that are about (3"-4") taller. That'll effectively reduce the highway revs by 10-15% (acting more like a 3.73 gear set). With the 3.06:1 low gear in the 700, you'll never notice a difference at the traffic light.

Food for thought anyway.