For gen II, since there is room for a second plug tube, couldn't you custom build an aluminum shell around the coil, then cut and weld the top and bottom of your spark plug tube to the shell? Then you wouldn't have to worry about fitting the whole works in a tube, just need to fit under the valve cover amongst the rocker assembly.

Something shaped like a muffler with the entrance and exit offset. Just need somebody with a TIG welder.