PHB vs. Watt's Link

[Norm Peterson]

I'm assuming that it's either a torque arm or 3-link arrangement that we're discussing, rather than the addition of another means of lateral constraint to the OE 4-link or a Satchell . . .

How about first deciding on where you want the rear roll center to be, and on how much ground clearance you need to maintain. That, in turn, depends on how much rear axle roll steer you want to end up with and the LCA inclinations (both plan and side views), and should be slightly higher than the front RCH. You may even want to start with some desired amount of anti-squat to get started from the LCA side view inclination.

100% anti-squat is your likely target if the dragstrip is particularly important, and perhaps half that for road course/auto-x/open road (in the interest of avoiding brake hop without giving away any rear braking contribution). Maybe shoot for 3% - 5% roll steer (vehicle understeer). IIRC, Katz's car has 2% and if your Chevelle's OE geometry is anywhere close to the G-body's it's about 8%. As a general guideline, 7% has been considered too high for best slalom performance. BTW, all of these numbers are at static ride height, and will vary somewhat over suspension travel.

If you're not quite sure where to spot the RCH, or want to retain the ability to fine-tune it later, a PHB that's adjustable for height would probably be easier to work up than a properly-done Watts with a similar feature.

Packaging is likely to favor the PHB, though the diagonal brace to the passenger side frame rail that you should be using* isn't without its own effects on things like exhaust routing.

*Without this brace your driver's side frame rail would be picking up a torsional moment in addition to the entire lateral force. With it, the lateral force is shared between the two rails (not quite equally, though) and the torsion is replaced by vertical forces.

Norm