If anyone knows where I could find one, or has one, please point me in that direction. Hoping to use this in my J1 box for my autocross car to eek out a few more mph in 2nd gear.

I am assuming the gears will swap onto the shafts of the J1 since I just did a diff and countershaft from a Y1 into a S1 box for a friend. This is kind of my only option with no aftermarket support for these units in gear choices and an LS 1.9 2nd gear being too long since it's an NA build, methinks.

 

You would need both the countershaft 2nd gear, as well as the actual mainshaft from the Y1. 1st, reverse, and 2nd gear are all machined into the mainshaft itself and cannot be changed independently.

I would just go with the LS 1.9. I have a Y1 trans with the 2.05 2nd. I wish it was a bit longer

But no, I will not swap it out just for that! lol although I am building a YS1. So maybe when I put that in.....

Also, if you have a J1 now then you should have a 2.1 2nd. The difference between a 2.1 and a 2.05 at 8k rpm is only 1.5 mph... hardly enough to even care about. The change to a 1.9 will give you another 6mph or so (dependent on tire size and actual max rpm, of course)