SHORTENED DRIVESHAFT FOR 1996 BLAZER

I have a 1996 4 door Blazer that is bagged and I keep pushin diff seals in. Just wondering if there are any other 4 door Blazer owners that are bagged that might know how much the driveshaft has to be shortened. Or how do I calculate how much it needs to be shortened?

Rayme ThomsonDROPSICLES