I believe the Boss 302 engines in '69-'70 could come with either the cast/finned aluminum covers, or, if they had stamped steel covers, they were chrome from the factory, not by the owner. However, I am not the last word in some of the details. Yes, the boss cars did have oil drippers spot welded to the undersides, that, I do know. There is also a difference in the stamping between the '69 and the '70 steel covers, most visually the corner by the oil cap differs, '69 is squared off, whereas the '70 is stamped with an indentation there. Either way, for real Boss covers should have the spotwelds slightly visable through the chrome plating on top. I am running a set of '70s on my '71 351c.
I think the 351 Cobra Jets came with oil dripper valve covers, but painted. I know the Boss 351 was fitted with the cast/finned covers, at least from what few I've ever seen.