I have a holley 5200, factory reman, still in the box. I'll give it up for $150 plus shipping. The weber adapter plate works, and yes you can find them all day on ebay for $40. As for the choke, depending on which 5200 you get, it will have different chokes. You can get manual, water, water/electric, and electric. You probably won't find a carb with an electric choke already, but it's an easy, cheap conversion with parts from the local parts store. Mine is a water choke if you're interested. You'll also need to rig something up for your throttle cable, so keep that in mind.
Here's a link with some more info:
http://www.mazdatruckin.com/B2200/5200.html