That is how we were taught to double team as well. (But then we were also taught to spear block for one season before it was outlawed,) I still do not think that a hi/low both from the front is that dangerous. Heck, I got hit from the D like that playing O many times. Now one going high in the front and one low from behind definitely is.
Another one from the old days.....when punting, many teams left a gap between the long snapper and the guards. We would have essentially 2 nose guards set a a 45 degree angle set in the gap....their sole responsibility was to fire into the long snapper from both sides. Needless to say, the long snaps got iffier as the game went on.