First things first. I'm assuming you're trying to install into
standard Combat Flight Simulator 3, not one of the expansions (ETO, MAW, Rising Sun etc)
If you installed the bombers correctly, they will each have a folder in
Combat Flight Simulator 3/aircraft. If the bombers have folders anywhere else, they won't show up in the sim. Any weapons, effects, pylons and sounds supplied with each download must also be correctly installed as per the Readme file in each download.
If that's correctly done, you need several other things installed before these models will work. Check the Readme file with each download, but you'll likely need the AvHistory Weapons and Effects installed too. They're in the Library here at SOH.
Bog standard CFS3, even though properly updated to 3.1a, has a strictly limited list of countries available for use. This makes models correctly assigned to, say, the US Navy, not show up in the sim. You need the Nationality Expansion Kit installed before you see USAF, USAAF, USN, Royal Navy, Italy etc as options.
That covers the usual problems. Let us know if you still have bother and
don't look for esoteric Windows 10 problems before you've checked and done the above: Win10 is often cited as the problem in many cases and 19 out of 20 it isn't that at all.
AvHistory Effects
AvHistory Weapons Pack
AvHistory Weapons and Effects Textures
Nationality Expansion Kit Redux
Hope this helps
!