Bill:
I have a Synchro 300, It is hard wired as it draws in excess of 120 amps, thats on a single phase circuit, and of course for full output, which you should not see often.
The connector you are looking for is a NEMA 50. It has the straight blades for power, one smaller than the other, and a D shaped ground lug. Avoid those home depot plastic cheapies, go to an electrical supply house.
If you plan on doing any aluminum you will need to go to a watercooled torch, you wont get too far with a gas cooled unit. Of course the torch needs a cooler, a cheap unit runs about $450-500.
You should be able to power your unit using a NEMA 50 plug and a 60 amp breaker in the box. just try to limit your cable length to the machine.
Also, if you buy a torch get one with 25' leads, you won't regret that.
There are also other things you might need, accessories and such, pm me if you need more info.
Cheers
Phil