ORIGINAL: ffkiwi
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.
Gordon Burford did it first with the Taipan 2.5 Goldhead back in '73, and the Blackhead 3.5 of around the same era
'ffkiwi'
Um, you may find that Taipan only had seperate upper barrels, not rotatable ones.
http://modelenginenews.org/cardfile/t25bbre.html