The only difference between the B and C models is the way the upper pivots attach and the zerk fittings on the C model.Found the pick up tubes.
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From what I can tell I'm just missing the follower. Not strictly necessary from what I can see. Fortunately the Dillon manual is very well written so getting its maintenance done should be straightforward.
I downloaded the 550C manual but I also found the original 550B manual. Doesn't seem to be too many differences so far.