I can't remember the brand of that panel as I have run into them before, the pullout on the far left is like an optional main which in the ones I have worked on was 100 amp with the flat blade contacts on each end of the fuse, it might be a Wadsworth, most 60 amp panels had two pullouts and 4 to 6 Edison base fuses where the 100 amp panels had two pullouts unless it had the separate main like this one, and had 8 to 12 Edison base fuses, the 200 amp ones had up to 4 pull outs would have 12 to 20 Edison base fuses, some were designed so you could add extra fuse blocks in groups of 4, I have found them in both commercial as well as dwellings some of the old beach houses around here that had all electric heating had 200 amp ones, I find it strange that the meter is fed from the tap box below it, those conductors look like 3/0 in it, the meter must have a conduit out the right side to the panel out of view, the left pullout of the two side by side looks like it feeds the added breaker panel.
The only way to know for sure is to pull out the far left main and see what size fuses are in it?