matching # car have build sheet,but not complete.actually have part of build sheet from under the rear seat,and allmost all of the build sheet under drivers seat.casting # on block is 3963512 and 1 11 70.looks like gm 8T and has a P on it.Block identification # T0104CPD 11B141720,that matches vin on car.Tonawanda plant jan 4th,.on build sheet it says baltimore maryland shipped to norfolk va.LS5 Z15 SS 454 Group.I have seen other build sheets that say Z15 ss 454 pakage why does mine say group.Is there any way to find out rather than droping the oil pan to see if it a ls-5 2 bolt main or a ls-6 4 bolt main. thanks joe

Well there is an easier way than dropping the pan because there were no LS6s available in '71 on the Chevelle (only Corvette). So if your car is a '71 454 it has to be an LS5.

matching # car have build sheet,but not complete.actually have part of build sheet from under the rear seat,and allmost all of the build sheet under drivers seat.casting # on block is 3963512 and 1 11 70.looks like gm 8T and has a P on it.Block identification # T0104CPD 11B141720,that matches vin on car.Tonawanda plant jan 4th,.on build sheet it says baltimore maryland shipped to norfolk va.LS5 Z15 SS 454 Group.I have seen other build sheets that say Z15 ss 454 pakage why does mine say group.Is there any way to find out rather than droping the oil pan to see if it a ls-5 2 bolt main or a ls-6 4 bolt main. thanks joe
Different plants used different wording sometimes, even within the same year. A Baltimore sheet I have for a 71 454 says (as yours) Z15 SS 454 GROUP and a KC 454 sheet says the same thing. But, two Van Nuys 454 sheets I have say different things, not only different from the Baltimore and KC sheets but from each other as well; one has Z15 SS 454 PKG and one has Z15 SS EQP PKG yet both are LS5 equipped.