ORIGINAL: earlwb

Hard to say, I don't know when MVVS started doing it. But the Fox .19 BB engine did it before they came out with the .25 BB engine. I think if I remember right, the .19BB engine came out circa 1985, and the .25BB came out in 1989.
Also the Fox Eagle II, III and IV engines all have a rotatable upper cylinder block too. I did have a couple of III's set up for reverse exhaust when I was doing pattern years ago. I also did a III for left hand exhaust for a twin engine plane a long time ago too. Duke Fox actually setup my pattern engines for me as I was maybe the first to do it and he wanted to be sure the tips of the piston ring wouldn't catch in a port at the time.