I thought it was primarily the vane section and liner of the Skat Trak pump that adds the weight as they are stainless, right? They are still going to be there from Skat Trak. Billet is denser than cast aluminum, so are you making your sleeve very thin to reduce weight, since billet has more strength than cast?
The liner is still the same with far less mass on the housing. (billet)
The billet housing is without the 3 flanges to bolt it together, and the long bolts are replaced by shortys.
and remember the stock pump has to be reinforced with welded 1/8" material to be a 148.
The loss of weight will be minimal, (maybe a lb). We'll let ya know