the 9 blade fan with the Horton clutch is a huge upgrade over the viscous clutch... I did it on m,y T-444E and the results are amazing.. you'll never begin to move enough air with an electric fan..
I thought the 4900 Radiator frames are much taller than the 4700s which are 3800s are based on.. and I think the FE busses are using the same size as the 3800s.
Be careful when shopping for fans and clutches, I believe the belt drives the back of the fan pulley on the 466E vs the front side like the mechanical or the T-444E which means you have a reverse rotating fan comoared to those other common engines..
ECCB has a later nodel IC/Amtran bus he recently sold to a friend of his.. it has a 466E and the full rad / CAC.. see if you can snag his VIN and get the rad / CAC part numbers from it.. my guess is those will fit your busses..