Carl, an EFM 350 or 520 will fit your needs. The tankless coil area is a common trouble spot on these boilers. If you go to look at a used one, make sure the coil area is in good shape, or has been properly repaired. Make sure the base isn't badly corroded from sitting on a damp floor, and look through the EFM stoker assembly threads in this forum so you know what parts should be included. Ask the seller what parts have been replaced, and see if they will "bench test" the stoker for you. A common stoker rebuild includes new burner plates, gaskets, gooseneck bushing, burner worm, burner tube, worm bushing, etc. There might be more or less parts required depending on what kind of shape the stoker is in, but that should give you a rough idea. Check the gearbox for tightness and smooth operation, and make sure the fan isn't bent.
Depending on the age of the boiler, there may be one or three baffles. The tube boilers have one cast iron baffle that hangs in the boiler. The plate boilers have two smaller baffles hanging or welded on the heat exchanger, and another baffle hanging at the top. Make sure the baffle(s) are included with the boiler, and not severely warped.