4 Speed ?
 

I'm learning more about the difference in transfer cases....now for transmissions.....How do I tell what type of 4 speed is in my truck? Is there a way to just look at it and know?
FYI= My truck is a 71 1/2 ton 4 speed with factory Lock outs and a 350.

To the best of my knowledge, the only 4 spd they used in a 71 1/2ton was the GM/Muncie SM465.

GENERALLY speaking, GM 4 speed models used were the SM420 up till 1967, with the SM465 taking over in 1968. The SM420 was never used mated to a 205 transfer case, while the SM465 was always married to a 205 case. There was only one year the 420 was married to a transfer case, 1967 when it was mated to a Rockwell T-221 case. This is info I have compiled, please, if someone else has any conflicting hard facts regarding my info, please post. :)

Yup, should be a 10 spline SM465 as stated.
Cast iron and lasts forever.
-- Mike

Sounds good...so I've got a SM465 4 speed and Np-205 T case....nice to finally know so I can either swap or rebuild, whenever I make up my mind!:D

NAPCO ken,
Interesting data, I have an SM465 married to a Rockwell T-221 that came out of a '68. That is the only contradiction that I can add.

I have an M465 mated to a Rockwell in a 69 K20. It might be an early 69 where they were trying to get rid of leftovers. I want to convert it to an NP205 to get the lever to the right of the shifter. Zoomy/Pappy

Interesting about the 465 to Rockwell 221 case...I wasn't sure just when the break in transfer cases was!! Thanks for the update for my records!!

early '69
 

My '69 GMC has a SM465 mated to a Rockwell T221.
It also has a closed knuckle Dana 44.

Originally had a 305 V-6 also.