Two 50A GFCI over One 5 Wire 60A Cable?

I just scored the attached for a song. I purchased the spa panel a few months ago, but today came across another 50A GFCI breaker and some 50A outlets at a salvage yard. Also included was a Hubbell 560R9W which is a 5 wire 60A water proof outlet.



Since the 560R9W is 5 wire, could I run Hot & Neutral to one 50A GFCI breaker on wire 1 & 2, then run another Hot & Neutral to the other 50A GFCI breaker on wire 3 & 4 and then share wire 5 as ground? It's a total of 100 Amps, but only 50 Amps on each wire. I would need to find a Hubbell 560P9W plug and a 5 wire cable which will not be cheap, but for a 55 Gal drum setup, it should be enough power for 4 5500 Watt elements to run at the same time.

That receptacle is for 60A 3 phase so I'm not sure that the individual terminals will support the loads you will have when used for single phase.
Also if you wanted to use one pole for both grounds it should be capable of carrying the total potential load. Not trying to rain on your parade, it all about being safe.

Each terminal would only have 50 amps on it, so they should be able to support the load.

I see lots of ground wires in cables that are much smaller than the load wires. I'm not sure why they can get away with it, but shouldn't the same logic apply here?

I have no idea, so I'm asking here before I commit to anything.

Since the 560R9W is 5 wire, could I run Hot & Neutral to one 50A GFCI breaker on wire 1 & 2

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You're missing a hot wire to each of these breakers.

You should have Hot 1, Hot 2, Neutral and ground going to each breaker (I'll assume you're powering elements and controls) which is 8 wires total using 6awg wire.

The Hubbell is cool and all, but I think it's time to set it aside . I would use 2 separate 50amp service runs from the main to the spa panel. If you are bringing 100amps from the main to what would now be a sub panel you are in another situation with I believe #4 copper or #2 aluminum.