IIRC, the old Motorola MC6821 PIA had bit-configurable I/O. Now, I wouldn't suggest using one of those, unless your 805x is very slow. However, I see that, on Opencores.org, there's a VHDL model of the 6821. You might not want to utiize the entire model, but the I/O portion might suit you, and, of course, you're free to increase or decrease the I/O's and feature set.

Would that address your need for bit-configurable I/O? If you use the model as-is, it might allow you to do some experimenting before you wade in and customize it to your needs. Further, with a 5-volt-tolerant CPLD or FPGA, you might find it fast enough and capable of handling your level-shifting need as well.

RE