>>5359894I think you should try for planelegs first. They're reasonably easy to mod from WW2 1/72 fighter jets and don't take quite as much planning as the full-body modifications. You'll still have to mod the fuselage and wings with putty and plasticard even with those, mind you, but that'll be reasonably hard if you use Tamiya-kits as a basis.
These here were based on Revell-kits on account of how cheap they are, but it ended up being so much work that I figured I might as well rescribe all the panels.
The B-17 in itself is an interesting subject for such a conversion, but I'd personally go for a B-17G with is underslung nose turret or a Model 299 with its turret on top of the cone. The main problem I see with all the bomber-conversions is that you need to have a really good idea in your head what the final product should look like and that you'll probably end up buying two or three kits of various scales to get everything you actually need.