Note, a PAL-Amiga switched to NTSC is still producing PAL only at 60Hz instead of 50Hz and vice versa.
That is not really relevant for a500/a2000 as they only have mono composite out anyway. So they are neither PAL or NTSC (neither are the RGB ports on any of the Amigas).
It was common to use NTSC to mean 60hz and PAL to mean 50hz (even AmigaOS does it). The official name of EIA 525/60 & CCIR 625/50 are not as catchy & haven't caught on.
Adding a 1mb agnus and a toggle switch is probably the easiest way if you want 1.3 compatibility. However if your monitor can't show both 50 & 60hz then you might as well just hard wire it. Or even just get the correct agnus for your region. The earlier agnus had a seperate 50 & 60hz part, which are often referred to erroneously as NTSC & PAL.
