Yeah mine had some wheels that stuck out when I got it too. Changed that out quickly.
The 5th gear in the transmission is what I swapped out with an RX7 tranny. same internal design just different gear ratios. I dont remember the exact gear ratio but on the freeway at 70mph my engine used to be around 4000rpm! now it sits around 2500rpm at 70mph.
the exposed gear on the right is the 5th gear. center and tail shaft housing were removed to get to it and swap it out. Did it about 5 years ago and this is the only pic I have left.
here is a link to the info page I used back when I did it