Spoke to the tech support line at Pfadt. Their bushings have grooves like the Global West design that allows the lube to move. They also use polished alum inserts to reduce friction, binding and the squeaking. You can also easily remove the alum inserts to re-lube if needed. The diameter and widths are stock GM rubber measurements. They have their poly bushings on several C5 and C6 vettes that are daily drivers with lots of miles - no squeaks or other problems. I'll order those.
Geez, who woulda thought bushings would be a tough choice ....
http://www.pfadtracing.com/products/...&search=&page=