The Full Floating 14 bolt CAN be converted to 6 lug, but it takes custom machining to do. If you do a search you can find info on the 14bff converted to 6 lug. Or like said earlier, you can convert the 14bsf to 6 lug. There are also 6 lug 14bsf available, they are under post 87 Chevy light duty 3/4 ton pickups. They will need to have the spring perches, and shock mounts moved to work in an older K5. There are probably also some other stuff needed too. Just not sure what they are.
My Chevy isn't broken, its just out of gas.