I happened to have NA power supplies for both the GVP and the A500, so no problem there, and I never tried to use a (NTSC) TV as a monitor.
I didn't know that. I can only imagine they weren't selling many A500's in America at the time. Rumour has it that the A500+ was released early because there was a shortage of A500's. Supposedly the only A500's available were on a ship, they had A500+'s sitting in a warehouse so they put them on a plane and of course they arrived first.
The agnus in the a500+ is jumpered between PAL/NTSC (either 5v/gnd, can't remember which is which). So it's not hard to convert them. You'll also have to use an NTSC modulator to output composite/RF for a TV (for some reason you don't get RGB inputs in your TV's ).
The only other difference is the keyboard, which you can steal from an A500.
That should be all you need to get an NTSC A500+. Quite why you'd want one is another matter
