Many thanks for your prompt and complete response, and for your suggestion about the Collins book. I have two quibbles.

First, you write of advowson that "the right consisted of being allowed to propose a candidate for a living, not the right to install one. The right to actually install was the perogative of the local bishop." While that might be technically true in canon law, query whether it was true in substance. My sense is that the bishop's right of installation was for practical purposes never exercised contrary to the patron's will, except perhaps in the case of a notoriously scandalous candidate. The quality of the Anglican clergy in the 18th century was too low, and the English respect for both property and patronage too high for it to have been otherwise.

Second, according to the source in my second post, it was unlawful for a clergyman to purchase for himself a next presentation. The existence and limits of that statute are arguably a recognition that the sale of next presentations is otherwise lawful.