School me on 3speed manual transmissions

I got a real good deal a few years back on a 3 speed manual that the owner said came from a '71 duster. Was there only 1 3speed man. trans or 2 versions of it? How much power can a 3speed manual trans take? I thinking one was light duty and the other was heavy duty? Here's a couple of pics so maybe some of you can help me id it.

Another if it helps at all??

Look & see if there's an "A230" on the machined pad at the left of the pic. I circle track raced one & no problems & the /6 & V8 ones had different ratios for 1st & 2nd. EDIT the A230 is heavy duty & 1st is synchronized. Holler if you need the ratios & I'll look them up