Hey Vern, I have a 1970 SS 396. It was sold at Mecum Dallas in September '14 as a rotisserie restoration of a rust-free New Mexico car, a 375 HP SS 396. The engine pad was restamped at some point, possibly during the restoration. The pad stamp of T 0503 CTY would be fine, except I'm told that GM stopped producing the L78 engine in October or November of '69...LOL. The block casting is correct, I believe at: 3969854, and I believe the date stamp on the passenger side of the bell housing to be D 2 9.
The heads have a half-moon shaped casting on the front of the heads, and there are two plugs (look to be about half an inch) just above the oil filter. Also, the car does have an aluminum intake manifold, #3963569. I'm thinking the engine is an L78? Am I understanding you correctly? By the way, I'm in College Station...where are you? Retired Army guy here. Thanks for any help you can give me in trying to figure out what is in my car. Best, Joe Northrop (979) 324-6432