The 93 (J2 Model) is THE KX250 motor in my opinion, it can be made for bottom end or top end power with just a few changes. If you are after top, keep the stock pipe as it pulls harder up top than any other pipe & I tried them all. If you are looking for more bottom & mid go with the FMF, but it takes away a lot of top & over rev.
The FMF pipe for the 93 (92 model also) is the K24, the K27 is for the 94 model as Fox has stated & the mounting for it is for the "New" style frame of 94, but it is the last of the "Big" exhaust port pipes.
I think there is an extra stock 93 model pipe at my shop as I am using the later style frames now, i will check if interested, but it is a "Top End" style pipe.
If you would like more info on the 93 motor, let us know what type of power you are looking for & sure we can help.
DoldGuy