Looks like very nice lathe indeed!
There is plenty of info about the fitting and it's not confusing at all

:
DIN standard infoAmerican A-1, A-2 etc infoAbout the only thing they have in common is the taper angle (1:4 or 7deg 7min 30sec)
The rest, ie PCD of the bolts, bolt sizes, taper dia, etc, etc all differ.
I have DIN 55021 #3 in my lathe and I doubt that A-1 3" chuck would fit on my lathe without problems (although never had a chance to try yet).
They are great apart from the fact that chucks etc, with back ends to suit and allow direct fitting on the spindle, are very expensive and not as common as other lot (here in UK), so one ends up using backplates anyway...
For you with A-1 and people with D1 it should be easier, because they are (being american I'd guess) a lot more common.
Chris