I am not 100% sure what your trying to do, but I also have a B4 not B4.1 and I did upgrade some things.

-The outdrive bearing are 9832 10x16 mm, these fit the 9826 transmission case which required the 9818 rear chassis plate. You will also need the upgraded outdrives because they are slightly larger for the new bearings #9852. You might want to replace the entire diff if you have the gear diff #9853. The B4.1 rear chassis plate it cut out a little more because the B4.1 tranny is a little bigger due to the 10x16 mm bearings. #3977 (3/16x3/8) are standard AE bearings. Same as the from wheels and the inside rear hubs, the B4.1 has larger outside bearing in the rear hubs because the outside bearing were exploding. The upgraded rear plastic hubs are #9730 and the outside bearing are #7935. The upgraded rear shock tower is #9572 (Plastic not carbon, carbon was never upgraded.