I once made the reverse, kinda, I used a older UART IC IM6402 to take the output from a tape reader (parallel) and convert to RS232, It should be possible to use an IC like this the other way around and input RS232 and convert to parallel data ( it has both transmit and recieve registers).
You would need to simulate the sprocket hole which is usually used for clocking the data, there should be a signal for this in a UART and also an input to simulate tape pause.
I believe the commercial ones also have an internal buffer.
Al
CNC, Mechatronics Integration and Custom Machine Design
“Logic will get you from A to B. Imagination will take you everywhere.”
Albert E.