Soooo late to the party with one of these… 
But I does love me dinosaurs… the question I have for the brains trust is…
Has anyone successfuly transplanted solid brass spring loaded pins into these to alleviate the twisted mag terminal spring syndrome with these units? 
Yup, this was a mod I did on many Blasters that were factory fitted with the flat blade style contacts.
There’s plenty of spring terminals available on the market, with the only thing to keep in mind is the diameter of the coil springs in relation to how much room is available to get them to fit and clear everything properly.
I’m sure that the only reason the manufacturer’s chose blade type contacts over spring terminals is simply because of how cramped and close together they are due to the small spaces the designs called for.
The later version of the j12 did away with spring terminals and just went with fixed terminal, no more catching the spring when slotting in the mag.
J12 also has a nice bit of extra material around the bevel gear that the J11 box didn’t for a bit of extra flex resistance. Might be worth seeing if any retailers have the later J12 box.
I was going to say this same thing… that the J11 might be cool, but the J12 AK74U is where it’s REALLY at! 
