Mahogany Bob
I’m far from being the leading expert on such matters but thankyou for the vote of confidence!
The problem your 747 will have is the length of its stick. On modern medium-long range missile combat, the aim is to launch your missile from as high and fast a platform as possible. It is also a good idea to be able to turn away ASAP once the missile is active and using its own radar. So your 747 could carry loads of missiles but would be dead from the first shot it received before it ever got a launch solution.
As for the validity of dog fighting, the fact that all Air Forces still train for it should tell you something. There is an argument that in the fifth gen world, the first time you get to ‘fight’ it will be in the visual arena with guns, once all other weapons have been expended. Basically, it’s better to train for it and know what to do if you need to, than to not train and have no idea what to do if the time ever came.
The other problem will be the number of fighters you have and the number of missiles they can carry. I know you might think that’s where your 747 comes in but it just wouldn’t survive long enough to be useful. If there were a way to re-arm your fighters in the air that would be a real step change!
BV