I'm guessing, but the booster MAY be a 3/4 or 1 ton unit, not sure though. MC looks correct for C10 in 68. Does it function? Doesn't look hacked together to me (especially if it works). Someone may have just added a larger booster, or a booster period. Does your SPID show a power brake option? If not, then the whole booster was added.
Depending on what your plans are, you can run what you have if it works. Probably not a bad ideal to at least replace the crusty MC with a new stocker, very inexpensive - I'd imagine the brake fluid could use a purge too if the inside of the MC looks like the outside. If booster NOT working, you could replace it with a stock C10 booster. On the other hand, if you're considering a disk conversion, you can pitch the whole thing and start with new MC/Booster/prop valve combo (current setup is a stock correct distrib block that serves as a means of providing the signal to the Brake light on the dash - if there was a pigtail connected to it, that is..
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