Just get an eb48.4, you can get a used one here for a good deal i'd imagine. the eb48 and nb48 have different a lot of different parts. you could convert a sct easier than the nb. the rear diff housing is offset different than the eb, it's not worth converting. you could also try selling the nb48.3 and using that towards a eb48.4. if money is an issue, check out towerhobbies and use coupons + easy pay, it will divide the payments across 3 months and there's no fee and free shipping. that's what i did when i bought a new eb and electronics for it, since motor, esc, etc. is expensive. but easy pay made it np... haha

they do share a lot of similar parts, but since you are changing to the .4, there really isn't anything you can salvage.