The differences are:
- number of scan lines
- vertical frequency
Running 200 scan lines (NTSC) with PAL frequency results in the 'cinemascope' border at the bottom. Note that these lines are scanned by Denise, but lacking display data they have background color. Software usually checks Vsync to check for NTSC/PAL.
Furthermore, PAL & NTSC Miggys own slightly different clock crystals (NTSC and PAL differ in horizontal frequency), but this only matters for additional video hardware (FF, genlocks, A2024).
Is it possible to open PAL screens when running this involuntary NTSC mode?
BTW: the additional wire is for transmitting the A20 line for addressing the 2nd MB. 68k pin 48 sounds pretty good, but maybe it's not connected on the '030 card in '030 mode. If you own a multimeter you should be able to measure 0 Ohms between the different connection points for the cable.