1. This forum already has an entire section devoted to LSx swaps, and carb swaps. This thread belongs there. Perhaps a moderator will move it.
2. There's essentially no advance--"vacuum" or "centrifugal" built into a TBI distributor with the automotive ignition module. Over 400 rpm, the computer controls the advance. No computer, no advance. Which is why "carb swaps" also generally include distributor swaps to one with the ancient 4-pin module, a vacuum canister, and weights 'n' springs. But then you've screwed-up the computer that controls the trans shifting, if the truck is new enough to have a 4L60E. But of course there's no mention of model year, or transmission type.
3. The ORIGINAL 3310 780cfm was a reasonable carb. The later 750cfm versions are cost-cut with straight-leg boosters instead of down-leg, rear metering plates instead of a proper rear metering block, etc. Still, they're popular. A 750 Q-jet tuned to the application would be SO much better than a 3310 in any form. But given the rest of the engine...TBI is better still.
4. You'd be lucky if you didn't have to INCREASE the jet size in a 3310. The crappy-breathing heads and low-rpm nature of the cam would have less signal to the overly-large carb venturis, requiring larger jets to get the same amount of fuel flow.
5. As said...fix the TBI so it runs right, leave the carb on the shelf in the garage. Removes lots of headaches ESPECIALLY if the truck has a 4L60E or 4L80E.