Bought a non-matching numbers 70 Chevelle SS clone, The second owner said he didn't have any paperwork saying it was a true SS so he believed it was a standard Chevelle, someone went to loads of trouble to clone it boxed lower controls arms, larger sway bars, SS dash cluster, correct hood per build date and bumpers parking and taillights. the badge placement is spot on down to the 1/16 of an inch. you can't tell where any original Chevelle moldings were around the windows. the motor however is another item. The block has been decked so there are no numbers on the pad either tab or on the one above the water pump, Rear of the block shows casting 3999289 Center of the rear block is cast CM10. on the left side of the block rear is 825 74, I haven't a clue. Any help would be appreciated.