No one mention Turbo Action ?
GER?
I learned the hard way on that way back when. Broke one GER(it sound like a box of glass), they replaced it and the replacement had 13% loss. I've been running a PTC for quite awhile.
One of my buddies tried a 10" 4000 GER in his turbo 400 in his 68 Pontiac because they were so cheap. He got lucky. It lasted many years with abused street/strip miles in a 10 sec all steel street car. Still worked great when he just sold it a few years ago. The car has changed hands & is still going strong today & is back up for sale again now from new owner #2.