I think hes talking about the front.
AFAIK 50" front springs is the max you can go without changing a bunch of other stuff. There are a few companies doing SAS kits. Most of them will lift 2"-4" with stock front 73-87 springs, witch are 47" long. Cajun4x4 (a member here and on fullsizegm) has a ORD kit with alcan 50" springs for a 4" lift. IIRC he got about 9" of lift out of those.
Rear springs for a 73-87 are 52" Rear springs on 88-98 are 63" and theres no way to make those work without extending the front of your frame forward, making your bumper stick out almost a foot from stock.
Personaly I have plans to build my own mounts using some of the vendors here.