I bought it at the op-shop for my husband but it's too big, so mine to play with! So far I have cut the arms and collar off, sewn up the arm holes and folded the top down to make a kind of yoke. I thought I'd keep the buttons down the front but it seems to sit nicely back-to-front like this.
All this was done with the boys rampaging so there was no measuring or pinning, I just sewed along existing lines and did the eyeball-measuring thing. Here's how I was repaid for my inattention: