Hi, thanks for all the help so far. People do sell lots of parts for these transmissions; I'm currently exchanging email with Novak (novak-adapt.com), as they seem to do a lot of business in SM420 parts for Jeep rock crawl people.
That's a great tip about the input shaft vs. output shaft bearing; it hadn't occurred to me that of course those two shafts spin at different speeds exactly in gears 1-3. However, those bearing surfaces look great, no clogs in the oil supply holes, etc. So, here's hoping it is just some other bearing. It occurrs to me that, since the chip is on the 2nd gear driving gear on the countershaft, that's not likely the source of the noise anyway.
I should have mentioned up front that I want to get this guy back on the road soon - my parents are visiting for Christmas, and I really want to drive them around in my truck. So, what the heck, I will do the rebuild on it, put in a good 2nd gear if I can, otherwise just see what happens.
I'll let you folks know how it turns out!
