A "Cosworth" block is a Pinto block, only difference is by the water pump, if genuine it will have 'YB', followed by a number.

Also by the dizzy there will be four numbers, these denote the bore tolerances, Cosworth asked that only grade 2 (and maybe 3 from memory) be delivered to them, so you want to see like 2222 for example, once rebored this is irrelevant anyway!

Martin