MSD makes a box to control a carbed LSx motor... but it will not control the transmission. Also, in my opinion, the main reason to swap to LSx is EFI and the OD transmission. You are forfeiting that swapping to carb...
http://www.msdignition.com/Products/...oth_Crank.aspx
Here is a complete wrecked truck for sale in Bakersfield...
http://bakersfield.craigslist.org/pts/5346840239.html
PS: Stay away from 1999 and 2000 truck motors. The first two years had issues. I would skip 2001 just to make sure and look for 2002 or newer.