Are we talking about a Static Discharge or an on going electrical shock as you touch it?
Interesting question... I can not give you a good Marantz answer... But as an EE that has studeid ESD some - Electro Static Discharge.
For ESD ..... Grounding the chasis to an earth ground or electrical system ground may actual make your ESD discharge more instensive because your system is now hard strapped to a ground. I will look a schematic tonight to see how the chasis is or is not isolated.... I would think it isolated and not connected to nuetral, because the AC plug is on these old units is not "keyed" in any way.
If you are getting an actual on going "shock".... that is very bad and indicates a major fault in the Primary side of the power supply....
Honestly, either way I would not gound the chassis.... If there is a fault some in the primary side...you may create a short to ground and smoke.... and if its simple ESD, you will most likely make it even worse....
ESD happens a lot more in winter....with forced hot air heat...very dry in the house... better to add a humidifier. Humidifier will even help your health.
johnk