$300 for a rebuild kit? Holley makes some of the best carburetors on the market and rebuild kits are only $30-50. If that.
You can buy a brand new Holley 350 for less. Or I have a couple of good Webers in my spare parts cabinet I'd part with one if it'll help you out... My whole Jeep has been low-budget, high-forethought to do the best I could with what I had... The Holley or Weber is a great option.
If you want a fair price on one of my Webers shoot me a pm! I'm listing a few of my things actually and you get first crack at the carb.
As for choosing the right carb, look online for a carb cfm calculator. It'll ask for a few engine details etc then spit out a number. My 4.2L i believe needed like 243cfm or 283 minimum, do the Holley 350 2bbl is dead on for these engines.