Peter,A simple rule is to match the pump with intended car model of the sump.i.e in this case 600 fiat.
Fiat 127 and A112 pumps are the easiest and newest to buy,you just fit your 600 pick up (as in your case).This rule stays true with all the variety of sumps and cars.
If the pickup base is scored,patiently file it flat by hand.Also if you have the depth in the pan,as is often the case,you can also use the sandwich plate.
As a footnote,the Abarth enlarged pickups allow extra oil to enter on a fully baffled sump,but when not properly baffled they also let in extra air under very hard cornering.Which of course we dont want.
It takes patience because the majority of replica sumps today are near-junk.Some are copies of copies and take lots of manipulation to fully fit correctly.
Finally ,oil pressure switches move between pump and block,dont ignore this either.Grant