Joe,
Please read the original post carefully:
"...how to get a PC to read the 9th bit..."

On the 8051 it's a doddle: It's directly accessible - just read RB8!
(or set TB8 for transmit).
No need to mess about with Parity!

mov scon,#030h ; Set serial mode 3 (9 bits 9th bit parity)

NO!
The 9th bit identifies an address byte - it is not a Parity bit!