I first used a Keyspan USA-49W 4-port USB to RS-232 adapter, which worked well enough with my PiDP-8, but it had intermittent, strange behavior when I used it with any of my newer Macs. Any other adapters on the market would not work at 110 baud. Another web surfing session turned up The Aetheric Message Machine Company, where a reasonable alternative was presented. They reprogrammed a Silicon Laboratories CP-2102 on a development board to operate at 45 baud to interface with an old teletype machine. I bought a couple of the CP-2102 development boards from Tayda Electronics and a couple of MAX3232 TTL to RS-232 adapter boards off ebay, and after programming the CP-2102’s, voila!, two 110 baud USB to RS-232 adapters. Note that many of the CP-2102 development boards purchased off ebay use clone CP-2102 chips and cannot be reprogrammed. I was lucky.