Half shaft bolt pattern questions

[chatas17]

I have a 67 912 and I finally found out I broke a tooth on a gear. I have a line on another 4spd trans and it has a 6 bolt "half shaft" (is that what you call them?) opposed to my 4 bolt "half shaft". I am curious if I can swap out the 6 bolt with my 4 bolt so I can mate the trans to my car without changing a bunch of parts. Are they the same splines so they can interchange? Any ideas? I think the other trans is from a 66.

Thanks,
Jim