Well, I still think crapulent works. Think of food as congregating in the belly. It's not the sickness itself that is congregating--it's the cause of the symptoms that's congregating.

Yes, it is the size of the congregation that's the point, but not necessarily the size of the body. It's the amount of food and drink congregated in the body that have brought about the condition that brings the doctor and patient together. [And it's not the house that Jack built.]

Again: "A doctor examining one of his more crapulent patients [i.e., a patient given to excessive eating and drinking] said to him, 'Your body is a temple [i.e., subtext: treat your body as a place of reverence] and your congregation is too large [i.e., subtext: your eating and drinking matter that enters your body is too large of an amount or too large of a congregation for this temple, your body].

With 'crapulence' the emphasis is on the amount of food/drink that enters the temple; the congregation itself is too large of an amount.

With 'corpulence,' as you pointed out, it's the size of the body itself that is too large and not necessarily the contents of the body/temple.

I think both terms do work, but if the crapulent is the one in the original text, I would not see it as an error.