Completely different bearing system on the idler, they use tapered rollers instead of bushings and they slide on a 34mm shaft, if you have a 38mm case you just use a 2mm bushing to adapt it over the 34mm shaft.Just read up on that. Probably wrong but it looks as tho it is built for a 4 speed and 34mm idler shaft, no?
The high gears start getting a little noisy around 85 MPH and anything over 95 MPH for an extended time they are a bit loud but I just turn up the radio, for most of my driving 75MPH or less they don’t make any more noise than my factory box.