LA Engines???

Those numbers are on the front of the block by the head. I found the casting # 286030-273-8...this casting numbers shows on mymopar as a 318, 66-71?? Does the 273 mean nothing or is this some end of year deal. This Dart was supposed to have the 235hp 273 original and this block is supposed to be the original..(according to the guy who wanted to sell it).