1990 C60 rear end options?

[reddog]

So it now appears that I have acquired another bus. A 1990 Chevrolet/Bluebird came available locally and I just couldn't pass it up. 9 row, 8.2 Detroit, 5 speed, Klam retarder, auto chains, 12K original miles. Runs and drives like a dream. After the 100 mile trip home and going over Cochetpa Pass (11000' or so), I started to think a 2 speed rear end would be nice. This bus was the school districts "Activity" bus, and seems to be geared fairly high (65 MPH at 2700 RPM). I'm going to crawl under it tomorrow to see what it has in it now, but in the meantime, anybody know what diff units came in these and what 2 speed options might be available?
Ironic that I live in the town that is where a bus crash in '72 lead to the prohibition of 2 speeds in school buses in many states...
Doug@8000'

[kotflb]

You'll have a more reliable bus if you go with a 7, 10, or 13 speed overdrive transmission instead.

[reddog]

Any thoughts on what trannies might be an easy replacement for the 5 speed I have now. I think it is a CL551 Clark. Thanks, Doug@8000'

[kotflb]

Any thoughts on what trannies might be an easy replacement for the 5 speed I have now. I think it is a CL551 Clark. Thanks, Doug@8000'

Reddog, my first choice would be a RoadRanger RTO 6610 for a 10 speed and second would be an RTO 6613 for a 13 speed. Both of these will bolt up to an SAE 2 bell housing and have a long history of dependability. And both are overdrive. It may be even possible that some truck transmission shops could convert the RTO 6613 to a double overdrive, but that may be overkill in a skoolie situation.