Power has become cheap and subs have changed a bunch. Used to be weak motors and small light cones and coils.. Needed a huge box to get bass, and fairly low powerhandling capabilties and requirements.. Amps werent' class D, electrical sytems on cars were MUCH weaker too since they didn't have built in electronics like you see today People often bought multiples and did isobaric setups to reduce box sizes. Kicker IIRC, was the first company to make a real car audio sub as we know them today. Putting a 12 in a 1.5 cubic ft box was unheard of before that.
As far as loud, the world record during this period at one point was in the 150's and was just a bunch of sealed subs in a wall, and that was NOT on a termlab, so it was probably upper 140's on todays meter.. Standards were def different, a 140 back then was like a 150 now.