A 6v truck can be as electrically reliable as a 12v truck. If you want to know how to make it reliable, I'll post links to previous posts.
If you want 12v in order to easily use 12v electricals, that is a different matter.
I know nothing about lowering a vehicle, but it seems to me that doing this by removing leaves from stock-style spring assembly is not a safe methodology.
What aspect of ride do you want to improve (by removing a leaf or two, or by other means)?
http://www.lmctruck.com/icatalog/ca/full.aspx?Page=34
