Engine choice is definatly influenced by legalities. Australian Design Rules (ADR's) changed early this year extremely limiting choice of allowable engines for new builds...
The ADR relating to exhausts( updated sometime in the 80's) talks not about side mounting, but rather, the limiting factor being where the gas exits. The words go something like.... If to the rear then ??? millimetres past the last body seam, and if to the side, to the right hand side only. It also talks about exiting a minimum distance (100mm?) past the last cabin opening, i.e door/window. obviously also heat shielding of any exposed exhaust.
The De-Type in ACT argued that if mounted under floor pan, the vehicle could not meet the minimum allowable ground clearance at its designed ride height. Side exhaust was allowed with apropriate heat shielding, though the exhaust tip had to point inward under the car. and 92? dba.
I had a good repore with the authorities here when I started mine in '90, and they filled me in on all the loop holes and the way they interperate the ADR's ( a big problem is that all states interperate them diferently). I got a letter of aproval in principal which locked each of us into an agreement on what will be registerable. This lead me to building a G-Force on a very modified Crown chassis as it then only needed to meet 1972 ADR's. I've ended up with jag rear, HQ front brakes, carby with leaded fuel, and legal side pipes pointing outward at 96 or 98 dba, soon to fit rack and pinion steering. Its not as refined as the newer generation cars but does me, 3rd in class hill climb and up the front of the class in sprints at the Nats must mean its not to bad.
So sometimes its a matter of what you know, who you know and how you can make the system work for you.
