At ClubFrontier.org, there is a member, "Hawairish," that is very knowledgeable regarding the rear axles on Hardbodies and Frontiers. You should get in touch with him as he can answer any of your questions. Here's one of his threads on a H190A to H233B swap on a 98 Frontier 2WD:
1998 Frontier 2WD H190A to H233B Axle Swap + LSD + Disc...
Sharing my recent/ongoing project on my 98 KC XE 5MT 2WD, which is swapping out the H190 axle for an H233B, and adding some other related goodies. I've seen similar swaps done before, but I approached this one a bit differently. This swap uses the following components: An H233B axle housing...
www.clubfrontier.org
