Was a couple of versions behind but I downloaded and updated to the current version. All went fine.
I deleted (moved actually, just in case things went wrong) my current terrain files went to update them online.
Went online to the mission arena. The terrain downloaded quickly in just a few secs and installed normally. The arena selection screen came up with a markedly resized clipboard. It was very small. Hard to read small. I resized it larger and went on to the other arenas to update the rest of the terrains.
GS4 Alpha update was the same experience. Few secs, installed, resized clipboard.
Capture the flag arena, ditto. The rate of time change is very fast in there! A day might go by in a minute. Very cool for seeing the change in the sky quickly. Night only lasts a few secs but that mirrors arena "real time" norms. Unlike the arenas it does go full dark. I think the stars and night sky look absolutely fabulous but my aversion to night in the game at least as it's currently set up is well documented.
Went to the AvA Alpha arena and it updated as the others with the clipboard thing again. I got an "invalid skin number" when I got to the tower but it was otherwise fine.
The special events arena was the only map that took more than a few secs to download but I'm sure it's because it's a much bigger map. Even so it only went about 30 secs. It updated as the others, again with the clipboard resizing.
I went back to the mission arena, went to the hangar and selected skin downloads. The p51D skin began downloading and installed as it normally would. I knew it wouldn't be available immediately so I quit to restart the game and see it. As far as I knew the skins were never immediately available on downloading them without a restart? That may be why some are having problems seeing it right away. Try restarting the game people. That AND that particular skin may not be available on every terrain. Skins can be enabled and disabled per terrain. If the skin has been downloaded but shows red in the hangar, you can't use it on that terrain. I think it's always been that way. If you can't see the skins, restart and try offline. If it downloaded it oughta be there to use.
On hitting the quit button from the arena selection screen the clipboard resized again at the main game screen. This time it was way big and I had to make it smaller to see the quit button there.
Restarting the game offline I went to the hangar to select the new 51 skin. No problem. Went to the runway to check it out. Looks great. However, and I don't know if this is a skinning thing or a game thing but IMO the bare skinned birds' reflective properties, as I've said before, need to be toned down a notch or two. It's too mirror like. As if it were glass and not metal. It should be shiny for sure, but not to the point I could read a menu off it and as it is you can see every nook and cranny on the runway pavement reflected on the side of the cowling. That don't seem right to me. Of course that just like, my opinion man (tm The Dude)! Everybody else's MMV. One man's shiny is another man's dull.
As to the head positions I use TIR and had reset all mine to "home" so I'm kinda useless there now.