I understand any player could be entered into the game at any position. If I put a 5'11" guard in as my center against a 6"10" player how is his defense affected by that matchup? Do the physical attributes of the players impact the game in any way?

Weight and Height are just window dressing. Height and weight do affect some of the starting ratings a player has, but they don't have any affect during the game.

It's a little silly though.  Match up advantages or disadvantages like that should have far more extreme repercussions than you'd probably see.

There are a lot of things in this game that probably should have a lot more impact than you'll probably see.

Playing a -5 doesn't have enough negative impact in terms of the other team's three point percentage going up significantly.

Playing uptempo doesn't have enough negative impact in terms of additional turnovers for the uptempo team, particularly against a team with good or great defensive players.

There are others; that's off the top of my head things I've noticed.