I ran across this link while getting my 3 speed overdrive working.
http://www.speedprint.com/Deves50/ Click the How to Resources on the left, then scroll down to Borg Warner overdrive link.
Has the Borg Warner Operation Manual, and the overdrive service pages from the Chevy Truck shop manual, and an article on re working the solenoid. All of these are available in PDF format, so you can view or print them out, like I did,so you can have your own paper manual for reference.
One of the most linked pages for the overdrives is the early burbs pages at
www.classictruckshop.com, for some reason these pages have dissapeared. However, the above posted link also has PDF versions of the Early Burbs Overdrive pages, for download.
At one point someone posted that a Portland Transmissions had rebuild kits for these overdrives, but I have not found an address or phone number for them, maybe someone could post it here.
I was lucky in that my Solenoid and Governor worked. I was just missing the kickdown switch, which I replaced with a DPDT switch in the dash, alows me to have the automatic functions of the overdrive, but I can also force the overdrive out when I need the power.