Cujo8 - Yes, it is an sm420 and the unit is not cheap. 3k, and that doesn't include having the driveline shortened which is another $200.
I'm driving it to Portland next Saturday to pick up my cleaned 261 block that I will be building this year and into next. I'll report the performance and mileage when I get back. After installing this O.D., I'm not sure I really need the 261, but I'm getting it anyway
It should help on the hills though, especially since it will be moderately warmed up
BTW, I'm a big fan of this O.D. as opposed to higher gears or a 5 speed because it lets your truck be the truck it was meant to be in the 1st place, but with optional improvement at your fingertips (or thumb).
