Dave, RTS on HZ is greatly over rated and many people don't fully understand what it actually is....

Basically most Holdens before HZ came out standard with cross ply tyres. HZ came standard with Radial tyres and the suspension "tuning" was basically upgraded bushings, a thicker front sway bar and the addition of a rear sway bar... If you are doing a body off restoration you would upgrade all the bushings with good aftermarket ones and fit some good aftermarket front and rear sway bars and shock absorbers... most if not all car tyres these days are Radials so your HQ to HX will handle as well if not better than standard HZ RTS anyway...

If I was doing a standard van build I'd go for a HQ chassis..... no rego problems fitting a 350 chev (particularly in Qld.) into one and you don't have to run it on gas only...