At one time I had both a sohc and dohc sitting in the garage, and since the dohc had a real nice looking exhaust I thought about swapping them over, but that's as far as I got, looking at it that is!
it looked as though the ports were spaced a bit differently, but with a little carefull spreading they'd work out. as far as actual size, I'm not sure.
not realy a dohc fan, so traded it off for another sohc, but it got stolen after I took it home and snagged the rear tire off it. Figure someone must have realy wanted it to steel it without a tire.
Ken.