Perfect fit! They're just dry assembled now, so I need to take the triples back off, grease the bearings up, and finish things up.
The stem on my T500 is about 25 mm diameter with a 30 mm shoulder that is 6 mm high for the lower bearing race. The upper bearing fits onto a shoulder on the adjusting ring, also 30 mm in diameter. I'll post a couple of pics later.
The bearing kit I used was from partsnmore.com. The box is green and is labeled "Parts Plus SSK100". The sidepanel says the bearings fit Kaw S1 250, S2 350, S3 400, H1 500, H2 750, KZ250A/400/440, KH250/400/500.
You can add 1970 Suz T500III to that list

No seals were included, so I'll use plenty of waterproof grease and try to avoid riding in the rain.
Debby