That I can't tell you sorry, FYI this is the LS series motor not the SBC, SBC typically refers to the gen 1 iron engines whereas the LS is Gen 3+ which was Aluminum block for car applications and iron block for trucks.
I can tell you however that my car weighs in at 3900lbs with half a tank of gas in it, as compared to the stock RS6 is listed as 4024 which I presume is a dry weight as that is the factory number. I have not had the opportunity to put a stock RS6 on my scales though so if anyone has I would be interested to know real weight. So somewhere between 100 and 250lbs lighter than stock.
My gut feel tells me the LS motor with accessories is close to the weight of the RS6 motor with the same accessories on. The major components are Aluminum, the intake is plastic and it has 3 less cams and related stuff in it.