This "problem" is far from exclusive to IM. As Stan pointed out, a LOT of people use CB engines. Any performance engine from anybody is going to have issues with getting to the plugs, especially the rear ones. I'd go so far as to state that ANY engine equipped with a one carb throat per barrel setup is going to have a problem here.
It's just the way it is when you take a basic economy car and triple the horsepower.