What alternator should I buy?

Dimming issue would go away if you did the relay conversion.

There is a member on here that sells kits or you can get them on ebay. Probably the single best modification you can do to improve your lighting. It will also improve the interior lighting and dash lights.

http://www.forabodiesonly.com/mopar/showthread.php?t=216514&highlight=headlight+relays&page=7

Try this thread first. There are other kits available on ebay as well. I have installed three sets and they work great.

I think you will find that this solves the problem rather than installing a new alternator. Unless you have added accessories that draw power the stock alt should be fine.

Good luck.