I remember when GH started using a 3-4-3 and we took a lot of teams by surprise and got some good results. I think it's worth a try.
But GH probably worked on it for several weeks on the training ground. When the lads turn up on Tuesday they can't realistically be expected to switching from a back 4 to a back 3.
Why? Football is a simple game, three centre backs supplemented by mobile wing backs is simple enough, leather plays on either side so should have no problem on the left side of three, same with hall on the right of the three....
Dens,clee,buzz have all played in that formation for us before
There is a reason no top European team play with 3 at the back, and it's the same reason why Villa (who do play 3 at the back) are going to get relegated.
Playing with Wing backs rather than genuine fullbacks leave you exposed to counter attacks down the flanks. Also if you play man marking against 2 strikers, it means who have one man spare who is effectively just acting as a sweeper/defensive cover not really marking anyone in particular, just covering a defensive zone and playing the opposition on side.
For me we need to play 4 at the back: with Doughty and Densmore playing either side of Leather and Havern.
I would also add that we play better when we have two players down a flank ie. Doughty and Clee / Densmore and Lawrie, who both like to double up when attacking and overlap. Over the past year and a half under sinnott, we have played out best football when we have attacked down the wings and that is partly due to the fact that Densmore and Doughty can overlap and put decent crosses in.