Ed Iskinderian (Isky cams) was just a few doors down from RC Engineering's first shop in Gardena California. By all accounts, Russ worked directly with Ed to design and test cams for him. Before 1973, RC recommended Isky cams, and they were called the Isky 315 and Isky 327 cams, sound familiar?
Around early 1973, these cams became RC cams in the catalog. Presumably, Russ negotiated an exclusive for these cams, like he did with other suppliers (like Venolia, then Arias for pistons)
I assume that Isky supplied RC with cams going forward, but I really do not there know for sure. There were certainly continual developments going on with cams, as at least one change in profile/specs was made across their cam list.
George