Let's get real. How could you "precision bomb" in a B-17?
Short answer is...you can't. I suspect part of the problem is a mis-match of aircraft capability to actual need which had its origins in the 1930s perception that "the bomber will always get through" coupled with Billy Mitchell's claims about precision attack of naval vessels. As late as 1941, the US Government believed in the "strategic deterrent" of the B-17 as demonstrated by the reinforcement of the Philippines that year in a failed attempt to cow Japan into limiting Tokyo's imperial aspirations. Japan had been using "heavy" bombers in China for years and was not intimidated.
When war came to America in December 1941, it was found that the B-17 was not the impregnable airborne battleship that pre-war planners seemed to perceive it as, indeed its early war operations were rather unsuccessful. Some of this revisionist understanding came from the RAF's usage of the B-17 which clearly showed that the bomber didn't always get through. The B-24 had some better features than the B-17, not least of which was a better bomb load, but it was harder to fly and there is anecdotal evidence that it was less resistant to combat damage than its Boeing stablemate. There was undoubtedly continued belief in the Norden bombsight as the ultimate extension of Billy Mitchell's belief in precision bombing but sufficient bombs had to be delivered on the target in a hostile environment, something that Mitchell's demonstrations never replicated.
It should also be observed that interwar expectations of the efficacy of "heavy" bombing were woefully over-optimistic. By early 1942, it was pretty clear that the B-17 didn't deliver sufficient explosive force at long ranges. Pre-war beliefs that small numbers of bombers (small by comparison with the 1000-bomber raids of 1944) carrying 2000lb of bombs each would paralyse a city proved to be totally inaccurate.
Fortunately for the USAAC, the solution to both the lack of delivered explosive force and the bomber not getting through to the target was the same - send over a large number of bombers flying together in formation to provide weight of bombs and mutually-supportive defensive firepower (although it took time to get that right, with different formations and considerable up-arming of defensive firepower in individual bombers). Of course the problem is that precision/accuracy pretty much disappears with the the large-formation approach.
Early 1940s technology could have implemented precision bombing more effectively, either using long-range dive bombers or by adopting the early Mosquito tactic of going in fast at low level. Neither approach was a silver bullet, though, and losses - particularly for the dive bombers - would have been high. There remain questions about whether the high-speed, unarmed "Mosquito approach" could have worked on the scale required for a sustained strategic bombing campaign - it would be great for taking out key components within a target system (eg hit the switching controls rather than plastering the entire railyard) but such targets are relatively easy to repair.
What is clear, though, is that the USAAF was saddled with the B-17/B-24 and Norden bombsight which, frankly, were not up to the expectations set for precision bombing even at that timeframe, and particularly not in the European theatre. It could be argued that the bomb load of the B-17 wasn't really sufficient for a strategic air campaign in 1942...although that's a drift from the main thrust of this thread. The B-17/B-24 + Norden combination did the job because they had to - it would take too long to overhaul doctrine, equipment and training to start a strategic bombing campaign commencing in early 1942.