Keep in mind that the tranny possibly has the 3.09 low; Which IMO is very desirable, as it let's you run a 3.23 rear. This gets you a 9.98 starter gear and cruise at 65mph= 2600 with 27s.
To get a 9.98 starter gear with the regular 2.66 box, would require a 3.73 rear. And then you would have to put up with a 3000rpm cruise.
If you had to run 3.23s with the regular box your starter-gear would be 8.59;which sucks with any cam over 220*@.050
I love my 3.09; 6500rpm equals 52plus mph with 27s, and 3.23s
The trunnion D/S takes a licking and wouldn't be the end of the world. To get rid of it requires a swap of the mainshaft and the extension housing.
That tranny is worth some coin, even if you just get it for the 3.09 gearset. At least it would be, for me.