It could be you have the unsynchronized transmission that was available before the SM420? The SM420 is synchronized, at least in the higher gears. I think the SM465 has better parts availability than the SM420, another plus for the newer version.

Try this one for the Application guide:
http://www.roadranger.com/ecm/idcplg?IdcService=GET_FILE&dID=137495

And this one for the instillation guide, probably the one you need most: http://www.roadranger.com/ecm/idcplg?IdcService=GET_FILE&dID=137499

If those don't work I'll email you the file. The Tech tip should be revised shortly to show these new links.
Grigg

Last edited by Grigg; 06/02/2008 2:01 AM.
•1951 GMC 250 in the Project Journals
•1948 Chevrolet 6400 - Detroit Diesel 4-53T - Roadranger 10 speed overdrive - 4 wheel disc brakes
•1952 Chevrolet 3800 pickup
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"First, get a clear notion of what you desire to accomplish, and then in all probability you will succeed in doing it..." -Henry Maudslay-