I don't have enough info for the fault current calculation, and frankly have never done one. The series rated board is fed with a 65k 600 amp breaker from a 3000 amp service, parallel 350s about 90' long. The other panel is 600a, parallel 350s about 30' long, fed from a 600 amp main (probably CL fuses, I'm not sure) in a 2000 amp main service.
The building with the 3000 amp gear is fed with a transformer that is not shared, but I'm not sure of the size. I'd guess 750kva. The building that's fed with the 2000 amp service likely shares a transformer with other buildings on the property so I have no clue what size it would be.
My job in both buildings is minor and requires the addition of several circuits. Given the nameplate data it's clear the panels require 22k breakers.
The seimans BL (10k) and the BLH (22k) look identical except for the label. The BLH breakers used to be grey I believe, but they're not anymore. And the BL-H breakers are twice the price.