Mark -
In addition to your Shop Manual, perhaps these links can help "unsuck" your SM420 ...

> 1949 Four-Speed Synchro-Mesh Transmission Overhaul Booklet

> Link to another manual - or possibly the same

Don't know if they will help. I know that I can't help you. The only thing that I ever did to my 420 was run it dry of gear oil. (Filled it up with Lucas 85w-140 and it survived!)

Good luck


- Lonnie
My '54 3104
Photos that I have shared on Stovebolt via PhotoBucket are no longer available. Please contact me if you want a photo from an old post.
lonniecook [at] aol [dot] com. I sold my '54 3104 12/12/2017, but I still visit Stovebolt.

OLD STUFF ... houses, furniture, cars, wine ... I love it all