Serial to 8-bit parallel and the reverse ought to be trivial. There have been Discrete Component Shift Registers to do such conversions since way back in the TTL Cookbook day. Such logic must be very advance by now, and is likely implemented in many of today's tiny Microprocessor kits. I haven't played with this stuff for over 20 years, but I can't imagine serial to parallel should be a consideration.

jonklos, thanks for that link! Pardon my curiosity, but what's the acronym LUN & how might it be problematic for the 68k Mac OS?