NTB really isn't the right place for a car like this when doing performance upgrades. They won't have the ready access to specs for non-OE parts. There are more specialized shops that can handle what you want them to do.
As far as the rear mounts, they are not incorrect. They gotta attach to the frame rails somehow, and then they have to have isolators for additional shock absorption. There is a mount in the rear that contains such a rubber piece that is shaped like a wheel with an inverted taper. So there ARE mounts.
Still, you gotta either find a performance shop or do it yourself. Or at least a trustworthy independent shop that knows what they're doing with a suspension.
'09 PSM G8 GT - OPG Intake, DOD-Delete w/ Stage 1C 218/229 .600 Lift 117.5LSA, Kooks 1 7/8 Mids, Solo Axle-Back w/ X-Pipe, SuperPro Bushings (Front and Rear). BMR Sway Bars (Red)
"If you want to criticize someone else's work, be sure that your own is in order first."