MLB reads in 4-3 Defense...HELP

I haven't coached it, but I played in it. I was a center, so I would get in trouble in practice if I stepped wrong and screwed up the MLB's reads. This is why I know they're keys.

I remember our MLB had some very simple keys:

(1) If center blocks away on DT -- fill (trap, counter, etc.),

(2) If center attacks me -- I scrape through him (backside arm rip) to my gap responsibility in the direction of his angle (we ran both the college and pro 4-3, so based on the slant called, this could be anywhere from the A gap to the C gap),

(3) High hat = pass.

That's a start (it clearly doesn't account for every blocking scheme), but I'd be interested to see how the 4-3 guys do it today.

We read the backs. If we get tight flow we attack down hill. If another body is in the gap we play over the top to the outside shoulder of the back. If the play is playside off tackle we attack the inside shoulder of back in the B / C gap. If it is full flow to the playside we fly to the ball. If the ball goes away and it is tight flow we attack down hill. If it goes off tackle we play the inside shoulder of the ball carrier in the B / C gap and if it is full flow we are flying.