The sprocket kit/chain I got on mine has the same weight as a 2 pulley with Torque limiter setup with the wide belt, just below 9 pounds.
You might want to get a steel Jackshaft instead of your aluminum one. The aluminum Jackshaft then becomes the weak link. If you blow your Jackshaft in the trail or deep in the backcountry, you're kinda ****ed and you need a tow back to the parking lot OR call the local Heli-Skiing operation for a quick air ride...
Way cheaper, more adjustability and less problems in the long run than Cog belt drive system. You only need to blow 2 belts to pay for more than the whole chain drive system...
If you don't have problems with the cog belt, you might want to leave it that way. Just keep in mind it's there the next time you have to buy a 200$ belt from Spécialités Industrielles Harvey !