Originally Posted by Chuck73080

Would you mind sharing your source for the 14 bolt?

I'm going to swap my rear also, although I want a 3.56 (my tires are 225X75R16, 29.3" Dia.} for 2388 RPM@75 MPH with Gear Vender OD, 3062 RPM without. My 396" SBC crate engine dynos at 460 ft lbs @2400.

Here's a link to a Spicer RPM calculator.

https://spicerparts.com/calculators/...rpm-calculator

The first gear syncronizer in the SM420 sounds good, mine only has 62,000 miles but it'll be out anyway so it may be worth an exam, and synchronizer addition.

Please let us know if you have pictures posted of your truck because I would love to see it.

Chuck73080