Hi Derek
I don't know the part numbers as it was a loaned B44 (JC's
)
I used to convert my S4. Its quite simple though
all you need to do is remove the center slipper unit & alloy housings complete from the S4 and fit the complete center unit from the B44.
When you fit the B44 unit, fit it with the slipper adjuster to the rear & re-drill the chassis to match up with the holes in the alloy housing.
Bolt it all down the replace the front & rear props with the B44 ones but put the front B44 shaft in the rear & the rear one in the front.
When the rear shaft is in the slipper unit dremel as much material as possible from the black plastic input cup (this gives you the clearance for the end of you Lipos!
Then all you need to do is fit some battery straps and your done, I used Track power 4800 lipos & it is tight but I had no problems when I ran it with the cells moving or hitting the shaft.
Hope that helps Mat