I have 91 non-turbo Stealth RT that needs a new engine. Can anyone recommend a vendor to purchase the engine from or a shop that will rebuild my engine in the Los Angeles area.

You can purchase a new shortblock from Mitsu, that might be your best bet. You can have your heads redone at any reputable machine shop and have a mechanic you trust reinstall it.

Try 3sx performance for parts.
Dynamic Racing is a good vendor as well.

i bought very little things for my car, i special ordered almos every thing