After considering this all disc clutchs are basically the same dimensions , they need to fit on generally the same shaft .
A 4 disc though being much wider then the 1-2 or 3 .
Looking at Bullers site and not having one in hand the hub apperes to be counter sunk to make room for the extra plates ,
hub design is also improved .
The drive side appears the same.
The tuffy gears are an improvement over the original design which tended to wear the bell out . Of course high horsepower use being the key advantage .