Be careful with cheap on-line BBC valves; OEMs had 3/8" valve stems while aftermarket are 11/32" and will fit a 351-C. I suppose one could have stock Ford iron guides bored out to 3/8" and gain considerable weight- which will limit rpms. Stem lengths also vary, making pushrod length a variable as well with such a combination. To use an adjustable valvetrain, the engine needs hardened pushrod guides so at least 3" of one end of all 16 pushrods will need to be hardened. Stock 351-C pushrods are not and will wear in two, while spreading steel scrapings throughout your engine. There are no cheap shortcuts in building a 351-C.
Check your "ss" valves for magnetism; some places weld ss heads to plain steel stems so some parts of such a valve will be magnetic. What we're advocating is NOT having a weld (and potential failure at speed) to deal with, not whether there's stainless in there or not. And there are some odd mixes of stainless steel that are no good for severe service like in an engine valve. A few will actually rust and are weakly magnetic. Far east backyard shops also make up their own "grades" of stainless and other metals that the SAE have never seen before. Name brands with years-long good reputations are best.