I have never heard of dub pulleys, I would do a smoothflow from www.ottperformance.com
Actually from what your saying you want to do, their stage 1 would suite you well.
I wouldnt go lower than a 2.9. The supercharger comes out of its efficiency range stock.
The m62 does not go out of its efficiency range until you go below 2.8.
I would do a 2.8 if its a DD, If not you can go smaller. A 2.7 will give you a increase in torque and a small increase in horsepower.
A 2.6 will give you even more torque.
Technically speaking a 2.8 is on the edge of overspinning the blower, although if you dont plan to drive it to 100,000 miles you wont ever see any problems going smaller lol.
2.8 is the smallest i would go without meth, With meth and 60's, Heat exchanger, dual pass, opt. B and a perfect tune i would say you would be fine with a 2.6.
Kepp in mind some of the highest numbers where back in the day with 2.5's with no cooling mods, Wasn't smart but it made power lol
Also if you dont mind me asking why do you want to do cams?
It has been proven stock cams with cam gears will make more power than any aftermarket cams on the lsj, Plus to get them setup right will be over a grand.
What brand CAI, headers, exhaust, high flow cat are you looking at?