Yeah, I saw those base plates, but they're not for the extended mags.
Note the picture below (far right):
As for the spring, I can't say that the standard 1911 mag spring would be suitable for competition use, it seemed to work fine - i.e. no jams or missed-feeds
But then again, I'm no competition shooter. Standard rapid fire is about as good as I could do. I wholeheartedly agree that would need more testing. I've given my prototype back to the fabricators with a few requested changes, based on the feedback in this thread. I'm going to keep using all standard (MEU) magazine components, so when I start releasing pictures, it's not going to immediately look 100% as I intend (I'm using an MEU lower to start...).
I'm going to focus the magazine on gas capacity, and not BB capacity, which will free up a lot of the lower 1/5 of the magazine for more gas - but I'm experimenting at this point, so who knows how the prototype will go.
I'd be interested in a competition shooter trying this new prototype out once I can do some initial testing. This one will use the same length (or close to) BB chamber so the spring should no longer be an issue. The goal with this is to try and get gas pressure as consistent as possible (or reduce the FPS drop) near the end of the standard 1911 mag BB capacity.
Now to the valve-key. The only thing I can think of is to make a custom key myself with the fill-valve key on one end, and the output-valve key on the other. I need to get an estimate as to the price of this work before I can give an accurate retail estimate.