I just ported some code over, and made the necessary adjustments for pin changes etc; code completely compiles. However this is the strange thing.

On the 1330 I had OSCCON = 0x70 to enable to 8MHz int osc. and PLLEN =0. Since this does not support the PLL, I've removed that line but OSCCON = 0x70 is showing up as 1.98kHz on RA6 when I use:

Update: Just realised, it should be Fosc/4 on RA6, and as such this is working.

Problem solved. I tried to define,

#define PIC18F1330
#define PIC18F4331

and use #ifdef...#endif's to swap between chips, but I don't think the compiler liked those names...