Vintage Calypso IV Aqua Lung Scuba Diving Regulator w/ SW Dolphin 3000psi gauge

Description

Vintage Calypso IV Aqua Lung Scuba Diving Regulator w/ SW Dolphin 3000psi gauge. I know nothing about diving so please examine photos carefully. Assume this is for parts cause i can't test.
This has some wear. The round thing that has the mouth piece attach has a small dent and the rubber thing that comes off of it(perhaps the mouthpiece) is cracking off but it looks like it is meant to be replaced.
The rest looks in ok condition with a little surface oxidation here and there. There is a gauge and i think the brand is SW Dolphin, the logo is a S W and a fish it say it is for 3000 psi but goes up to 3500 on the gauge.
Message with any questions you can't get answered from the photos.