That's true. I wonder if it would be possible, since these are just rectifiers as in huge diodes, to find the schematic and then substitute modern diodes for each of the old ones. Just wire them in the same way.. it would still be a far more efficient charging system than a generator, and 100 amp diodes aren't tough to find or expensive, as in these.. https://www.ebay.com/itm/1141628294...ustomid=8c6d3ef8865313622af658aaaa605579

Regarding the regulator, is it solid state? Even if it isn't, one big advantage of the alternator is that the regulator only has to switch field current, only a few amperes, versus output current. Since you probably aren't daily driving the rig, it will last a long time yet.

1965 C60 school bus | 1967 GMC 6500 school bus