Looking for a little help from the Muncie transmission guru’s.

The M21 Muncie 4-speed (not oem to the truck) in my ’65 C10 has a broken reverse shift stud. Is it possible to drill and tap the reverse shaft or is it a hardened part?:
(1963-1965 vintage M21: Main case 3851325, Tail Housing 3846429, Side Cover 3831707)

http://i645.photobucket.com/albums/...%20Transmission/DSCF1810_zpsf7f3c46b.jpg

http://i645.photobucket.com/albums/...%20Transmission/DSCF1808_zps21ad2b2b.jpg

I have a spare M-21 which is a newer vintage M21 (‘68-’70). I bought it about 15 years ago, don’t know much about its history. Funny thing is it also has the side stud style shift arms, except for reverse, which has a bolt in it. Does this seem "factory correct" or is this more likely to be a modification from a previous owner ?
(68-70 vintage M21: Main case 3925660, Tail Housing 3857584, Side Cover 3950306)

http://i645.photobucket.com/albums/...%20Transmission/DSCF1818_zps3b449d2c.jpg

http://i645.photobucket.com/albums/...%20Transmission/DSCF1817_zps38a4f93c.jpg

In the Stovebolt Gallery ~~ "The Orange Crate" 1965 C10 SWB Step Side Build Thread

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