On Friday, September 14, 2018 at 8:51:18 AM UTC-7, John Foster wrote:
Does anyone know the specifics of what kind of regulator is used with the Older MH EDS systems? I’ve been given an older EDS unit but will have to buy a separate oxygen bottle and regulator.

I have flown a glider with a Nelson (adjustable) regulator, with the pressure dialed down to the specs (that were, may still be) on the MH website.
But there's a reason the old ones are being given away. Perhaps use it as trade in on a new complete system.
Jim