Never liked 3 at the back. Unless players are very tactically adept, with nous and pace in the back 3 and 2 very willing wing backs, it rarely works for long. Even if you have them, if one is injured there is unlikely to be a like for like replacement. The opposition will find space in behind at some point.
I don't think the Cowleys will go for this. Too much of a change in method. Stick to a solid base of a back 4. Then work on either 4-4-2; 4-3-3 or even 4-2-3-1.