So if I use the AE conversion kit for the RC8B, it will or it won't be very well balanced?
that will depend on battery choice.
I used the RCPD conversion for my RC8, and it was biased to the battery side, but handling was still really good, nothing that I noticed in racing it as far as bias goes, and I run a heavy batttery pack.
If you are really concerned about chassis balance, then you may want to look into the losi 8ight or some of the other kits out there like the Caster Fusion or Hyper 9E. The caster does a good job with balance since it runs a saddle style pack setup, and the Hyper 9E is quite narrow and moves the center diff back so more weight is towards the center of the car than say the RC8e.