Hi Sean,
You have a flair for understatement, "slightly modified" It looks modified for all get out to me.
Question1. Why are you putting in LCD defines if you are using the USART, Do you want dual display?

Question 2. Since you did not specify which PIC you are using, which port is your PIC equipped to use the USART ? Is it the same as the keypad uses?

Question 3. Why did you change the value of the resistors ? I suspect Bruce proved out his design before posting it on his website.