Trekkie- Did you mean to say that the units with the neutral bonded to the frame are SDS? I hope so. That's the issue here, if the neutral is bonded o the frame at the generator and the utility neutral is bonded at another location, then one would have to switch the neutral and hots at the transfer switch. The trick is to make sure the neutral is lifted from the frame of the generator if the service is bonded (as it would be) so you don't have to switch the neutral.
Generac and Onan do a good job of handling the neutral for this type of installation. Kohler on the other hand does nothing for their customers in the way of assisting them with this issue.
