220v 2 wire 50hz to 220 3 wire usa transformer

What Atlas sells is a unit that is modified on demand by the Atlas system given variations in voltage conditions on incoming line voltage. The system coordinates with a series of contactors to entice the transformer to behave in different manners.

It's not clear to me that you can change frequency with a pure transformer as you'll need a DC transition in the system somewhere...???

But it would seem that the wrong frequency might booger up the transistors within the appliance, no?

This isn't quite right, in USA there is no neutral for 240Vac split phase. The 3-wire conductor will be L1 L2 GND to the load. Shore supply uses 4-conductor with N only for the 120Vac loads on either leg.

I've often supplied 240V split phase to European equipment labeled for 220-240V single phase L/N input without issues. As long as the frequency difference is acceptable, a transformer is not needed to power the A/C compressors and pumps. And if the frequency difference is not acceptable, a simple step-up/down transformer won't help anyway.

A buddy with an Italian built trawler has two large inverters in the ER. Dock power goes to the inverters then out to the boat systems. They could be transformers but he called them inverters.

The boat also has Iveco engines that no one wants to work on.

Pascal, actually not only you can, at least with Victron inverters (which are very popular in Europe), but you should.
In fact, they are designed to work also for topping up shore power in the event of peak loads, adding AC generated from the batteries.
To provide this functionality, shore power must be wired to the inverter(s) first, with AC passing through the inverter(s) before going to the onboard AC circuit.
This way, if for instance you have only 32A or whatever available from the dock, you can set that limit for dockside drawing, avoiding to trip the pedestal breaker.
And whenever more than 32 amps of AC is demanded (typically, upon airco compressors startup), the inverters add it to the dockside 32A by drawing currrent from the batteries.
At least, up to a limit - that can also be set, obviously.

That said, the thread subject is actually different, and involves something (voltage + frequency conversion) that I don't think the Victron inverters I have in mind can handle.
But they are very sophisticated units, with plenty of functionalities aside from the one I just explained, so I wouldn't be surprised if there's something they can do that I'm not aware of.

You're referring to the new generation of inverter/chargers with features like AC pass-through as standard. Victron and others can also 'power-assist' the incoming AC supply for intermittent peak loads like motor start-up.

But @Pascal is correct, inverters do exactly what he said

Apologies if I've missed something in your question, but I'd connect L1 L2 to L/N and GND to case or green screw.

Ensure your N is not connected to the main neutral bus if the rest of your power is single phase.