is it just me, or does that transmission look a little funny to be in an E body?( no rear mount)
I believe even the three speed needed the rear mount for the shifter, front mount for the B body.
I can't swear to it though. The driver sits further back in an E body, hence the shifter sits back as well.
Are your eyes failing you? Both pictures in post one show the two mounts on the side of the transmission. That should tell you it's an e-body or a 71 to 74 b-body.
