Question What regulators are these?

[SaltyWombat]

A dive buddy donated these old regs to me to practice on after taking @rsingler 's reg service class. The two on the left look identical. Those two plus the one in the center are argon regs. The Scubapro on the right was likely used as an argon reg too and appears to be a Mk2, but I'm not sure.

Any ideas?

 

[SubseaSports]

The one on the right looks to be a MK2 as you say.
The middle one is an older Dive Rite argon reg.
The two on the left I haven't seen before.