I think Guys like BoB Pelikan & his RotoHak
are on the right track, building a chassis from the ground up and locating the engine where it makes the most sense, Yes on a road going Hack, center of mass is not as critical as it is on a "Dirt traveling" machine
Two wheel drive, A-arm suspension, All the power you will ever need, what else you want....???
Well a Motor seating three feet more forward will be nicer, but who is counting
Also about a year ago Scoot our sidecar guru post a picture of a European sidecar that was ready to compete at the dakar with a similar set up, rear engine, two wheel drive, big tank where the engine used to be but I can not find the picture to save my life..