If you have no emissions to worry about, you generally have 2 options: A replacement stock Mikuni or a Weber conversion. There are pro's and con's to both and there are really good discussions about them on here if you search the forum.

In a nutshell:

The Mikuni is reliable, better in below-freezing temperatures, and engineered to work at extreme angles. The bad news is that it doesn't make a lot of power, it's complicated, and it's more expensive to replace (and nearly impossible to fix if it stops working right).

The Weber makes more power, it's simple & cheap(er), and it's easy to fix/replace parts. The bad news is that may require more adjustment, it's not heated with engine coolant (may freeze up in very cold conditions), and it's been known to not work when the truck is tipped over at extreme angles.

Hope that helps alittle.