Porting code written for mega to pro mini

Hi, I have built a Ford CD Changer emulator from instructions found on the instructables web site, the project is herehttp://www.instructables.com/id/Ford-CD-Emulator-Arduino-Mega/.

I would like to port the code onto a pro mini. The problem is that when I change the board type in the IDE to pro mini it does not compile and gives me loads of errors relating to serial comms I think. I know the pro mini has RX & TX pins which I assume I can use to talk to my MAX485 chip and once I have programmed the board I won't need it to talk to my PC anymore, problem is the pro mini does not use the required libraries the mega is using to use its additional ports.

My question is this, can I do away with using the extra ports and simply rewrite the code to use the pro mini primary serial port? The guy who wrote the tutorial says that you need to use port blocking but I can't find any related help on this and I don't know what that is. I don't mind reading and researching but I need a bit of help directing my studies, can anyone help please?

Ok, the guy who wrote the instructable has kindly written the code for the pro mini for me, we had an issue with PC0 not being declared but he has now used PCINT8 instead, I really need to read up on ports, bit masks and the like, this one seems to be solved for now though, thanks for anyone who took the time to read it.