1/ 16780. This is the MODE for inverted 2400 baud right?
Correct
2/ The 'inverted' baud. Is that just keeping the transmit voltage level from pc - PIC at TTL levels 0 and +5v, instead of + or - 12v as used it RS232?
Nope, inverted means 1 is 0 and 0 is 1.
It is still 0 to +5.

What I can see of your code on my phone it looks like it should work.