Oh yea, these are standards for many types of saltwater fishing. The designs have changed from the older ones though. First they went to aluminum spools and flat aluminum cross bars, instead of the round tubular bars. More recently they went to a one piece aluminum frame. These changes were made because Penn finally saw what other reel manufacturers and the "upgrade kits" were doing. There's an outfit called Accurate Manufacturing that makes all these conversion kits for Penn reels, out of aircraft grade aluminum.
website:
Accurate
The tuna fishermen in So Cal are just fanatical about these conversions. This reel seller Berinson has lots of good pictures of the different Penns before & after conversions:
Berinsons
With all the high-tech competition from other reel manufacturers like Shimano and Pro Gear, the base Penn models upgraded with these kits are probably used more than any other reels in the So Cal / Mexico / long range fisheries.
Now whatever you do, DON'T start looking at these on e-bay; it will become a bad habit.
OK, if you really want to, just put in "penn accurate" in the search field. Have fun....