The requester chest's filters are dynamically set so that the assembly machines can each receive materials. The belts and output chest are monitored so that no item is overproduced. Additionally, the inserters to the assembly machines have to be connected so that a machine won't take all the items from items further down the belt.
This is an inefficient solution to a niche problem, but I hope it helps someone.
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JE3Y63NRGoiAtzjTsXpaF1SZxFwV/NjMe2/CiYDeUIh8C1wVLoU5Ynb/ZhabZheizC421C33Ccv1NbYamNtWnNoNVmzlhre6mtoymNt2nNotVmz1h1e6mtpymNtOnNux8XrgTFhF+dbVFlc8+tfXN5wV2Pi+yExYSbmqjlWHwzpTjmOhnC42YiTZsNmtlofIwqXwsn0efe3ZWy3nRWRzV4TNEbT31c+7f74f78nAtcb4tVlW5aJopvBXVem8WmdAul84pl5tMv7//H8d4uYQ=