I just clicked the link and it works for me. However, my high-end notebook that recently died sometimes had the problem of not being able to follow links that others could, so I'm not surprised about PC glitches. I probably have some windows pack that you don't have installed. I had to install a couple to get my copy of ACD Systems Canvas 15 to be able to save in jpg format, and maybe that's the difference.
Either way, most WWII fighters I an familiar with (most of the US planes at least, and several British and Japanese) have very limited inverted capabilities.
In the case of the P-51 Mustang, the horseman are a 3-man aerobatic team that make it look easy. If you Google one their performances, you'll note it is all positive g except for momentary negative to reposition.
Here's one of their performances using three Navy planes ... all with R-2800's like the F6F has.
View: https://www.youtube.com/watch?v=Gy9t8tK5yq8
It's all positive g.