It is originally a 225 Slant 6 w/ a 904 trans and a 7 1/4 rear end. They are all there. I think i am the 3rd owner or so judging by the title and the info I received from the guy I bought it from.
I still have to reasearch all of this, of course, but I'm a little too busy welding together body parts to take the time to find out! LOL.
Anyway, I don't know how rare it is, but I will find out eventually. There are probably some numbers on how many were built with an original Slant Six somewhere...