Similar story with my 78 W200. My grandfather ordered it with a 400 big block. However, the factory called him three weeks after they’d began bukding it, they’d run out of big block cores. So they offered him the same 360 that was being out in the LRE, plus a cash deal. So he got a factory 4 barrel, 360 4/spd. Even sent him a letter which I have a copy of somewhere