KZ550 Ltd- just for the wheels!!

Depends on the year and location. Once again, be careful, there are a slew of different brake diameters for the 400/500/550 line.

According to the Kawasaki Factory service manual:
In 1979, the 500B1 for Europe and Australia had dual front disks. They were 232mm.
Everywhere else got single disk. It was 250mm.
1980 was same.

(Rear disk was 237mm for both bikes, which is in-between for comparison.)

As I said, the forks have holders for calipers on both sides even if the bike only came with one brake. But the forks will be different from dual disk models.

In 1980 there is a 400 model:
UK and West germany got dual disk 232mm.
Japan and elsewhere was single disk 250mm.

1980 550A models:
European got dual disk 232mm.
Elsewhere single 250mm.

1980 550C model:
European got dual disk 226mm.
Elsewhere single 236mm.

1981 500B3:
Now all have dual disk 226mm.
Rear is 226mm.

1981 400J2
UK and West German dual disk 226mm
Elsewhere single 236mm

1981 550A2 same as 400J2
1981 550C2 same as 400J2
1981 550B2 same as 500B3
1981 550D1 same as 500B3

The forks use different amounts of oil too.

I don't know what models you would have gotten in Uruguay. Are they the U.S. models? Or were there South American models?