"In this age of technology, I have found that the internet can only go so far without making a phone call or putting your hands/eyeballs on the real thing.
I tossed a lot of budget stuff on my cherokee, perhaps you will be just as successful if you choose to go the repair route. Here are some ideas:
1) Get some pictures of your axles/broken parts you want to replace (crawl under that bad boy!)
2) As you are taking pics, get notes of all the part numbers and specific model names
3) Try to find out the specific model you have 1991 Isuzu Rodeo (LX?DX?Other?), Engine size, transmission type
4) Some axles have model numbers and gear ratios stamped right on them
5) Google those part numbers specifically... might find a match
6) Google Junk yards/Pull and Pays. Give em a call see if they have Rodeos/Passports in your production years, they probably will not tell you what is on them for parts you have to look in person
8) Narrow down to your specific vehicle... perhaps...
Planetisuzoo
9) Check CL for your specific model parts in a search.. sometimes a hit
IMHO.... Don't worry too much about an upgrade atm... the upgrade starts with it running successfully"