Well I have an update, and credit where credit is due. I took the sway bar to Stewart at APC, and we measured the bar and bushings, and compared them to the real-deal OEM bushings. Basically, the OEM bushings are a bit tighter, but they still slide off and on. There's no more than 0.05mm difference in the ID of the aftermarket polyurethane bushings and the OEM bushings. So in the end, it's not Centerline's product that is all wrong--it's my sway bar!!
Stewart didn't like the idea of using JB Weld, and recommended Loctite instead. Seems reasonable--Loctite will fill better, whereas JB Weld may get a squished around and not be where it's supposed to be. I imagine over time that the two components will bond together anyway---the gap is less than .5mm on a side.
Stacy Faught -- Alfas: 1983 GTV-6 (3.5l), 2018 Giulia Quadrifoglio. Non-Alfas: 1991 Corvette ZR-1 (500+hp Haibeck-built 32v 5.7l)