先说明我没有这本书，纯粹从你的题目所推导出来的答案。
另外，回复纯粹热心，毕竟功力不是很强，若有错误，
再请海涵与指正。
这句原本句子应该是这样，
He had considered overseeing the project's progress to be
his top priority until he was transferred to another branch.
但 to be是可以省略的，所以：
He had considered overseeing the project's progress his
top priority until he was transferred to another branch.
借由被动修改后，变成原题目。
Overseeing the project's progress had been considered his
top priority until he was transferred to another branch.
至于你问到的被动语之后不是不能加受词his top priority？
其实原因，主要是因为consider是不完全及物动词，需要在受词之后，
加名词或形容词做受词补语，而使语意完全。
例如longman字典，以被动语句所写的范例如下：
Liz Quinn was considered an excellent teacher.
至于剩下时态的文法题，整句语意应该是
监管计画的进展已经被他视为首要优先考量，直到他被转到分公司。
副词子句的直到...，是后发生的事，作者用过去式。
主要句子是直到...发生之前的事，所以比过去更早，可以用过去完成式。