Do we have the personnel for a Shanahan/McVay offense?

I think too much gets made of this. Any good coach caters his offense to what his personnel is, regardless of scheme.

Obviously you want good players everywhere, but you don’t have to have match player for player, skill-set for skill-set exactly what SF/LAR has at every position for the system to work.
I think it is the opposite (though you have a valid point), you have a scheme and you find the players to fit your scheme. It leads to why a player can dominate on one team then cash in with another team and under perform simply because he was a player in the right scheme which ultimately benefits both the coordinator of that scheme and the player, but if said player leaves and the coach thinks he can find a player to plug into his scheme and that player under performs in his scheme it is more than likely for the same reason the player he is trying to replace is under performing on his new team.

Its why CSP would always talk about "skillset" when he spoke on personnel.