I see things that suggest it's a Z1 lower case, cylinders and valve cover. I can't read the embossment on the lower right corner but there is no brace above the stamp, which tells me it's a Z1 cylinder set. If you look at the lower right corner of the bottom case you see only one case bolt. Later cases (from roughly mid 1974 onwards) had two. The valve cover has rounded ends. This was the Z1 style. From '77 onwards they had a rounded end but with a distinctive semi-circle on the end.
The engine has a single brace behind the serial stamping, which means it's not a MK2. But it has a Z1A serial number and also has the oil capacity scribed on a plate, so it's not a Z1 upper case.
Overall, to me it looks like a replacement upper case on a Z1 engine.
I'm in Canada too. (Near Kamloops) Where are you located?
I have a couple of Z1B's restored, an '80 KZ1000LTD restored, a 1981 KZ550 restored and a 2008 KLR 650 for off road fun. My wife has a 2019 Suzuki DR 650 for on and off road.