SB 360 which cam

I also would use the Lunati cam. Between the 2 intakes, I would run the Air-Gap unless your driving the truck in the cold. The LD-340 will have a good advantage in the cold.

I agree with your machinest on the smaller carb since the HP difference will only be about 10 HP on the big end. The larger carb, by compare, will be a little harder to tune, have less drivabilty, poorer gas mileage. This is only a marginal difference, but one that is there.

Since your running ported heads, the extra carb CFM would be a small bennifit.

The smaller carb will have increased velocity for better fuel atomization keeping torque up, excellent throttle response and best mileage will result.

With either carb you go with, tuning is of the upmost importance. If your going to go with the smaller carb, I myself have found good results with a stub stack from K&N and a open air cleaner and open top. This combo helps the carb breath better drawing air stright down from the top. (This actually will add a few CFM to the carb.)
Also a small note, if your driving in the cold weather, a full stock aircleaner is the best idea with a heat stove to it to help warm up the engine/carb for drivailty. You can get a 340/360 4bbl. air cleaner with a K&N or equal filter easy enuff.

I have run this combo of parts before. KB-107's @ zero deck and 2.02 J heads on 93 octane. If your pistons are below zero deck a little, the ratio will be slightly less and he octane requirement drops making it easier to fuel up and drive.

Lifter pre-loading is measuring the lifter being pushed downward buy the pushrod. There is alot of play in this area. IF the engine block was not decked, stock length pushrods will do. IF you want to measure with adjustable pushrods, look for a set of measuring pushrods with a marked shaft which will tell/show you the measurement as you adjust them.

Your looking for a min. of .020 lifter depressed downwards. Not more than .080.