Is the transmission a sm420 like the chevrolet trucks?

see here if it is the same as the chevrolet:

https://www.stovebolt.com/ubbthreads/ubbthreads.php/topics/700011/1.html


Fill is on the passenger side half way up the case. Or take off the shift rod and fill there but you probably still need to take out the side plug so you fill it to the correct level (bottom of the fill plug hole)