Your picture tells a thousand words.
The earlier pictures looked like the switch was a DPDT switch. In reality, it's a SPDT switch, and the Spektrum folk have added a small PWB to it so that they can solder wires to circuit board traces instead of having to wrap and solder on posts. That makes the service center's job much easier, they pop off the little board, and solder it to a new switch. Cool manufacturing idea.
So to your point, the Big SPDT switch you have will work, as the original AND the replacement are both single pole double throw switches.
I am surprised that the hole in the transmitter case is large enough to allow the new, bigger switch to fit, but if it does, it does. Again, your pictures don't show the old and new side by side, maybe the new switch has the smaller shank like the Jewel switch. From the size of the body of the replacement, I assumed it was a larger 1/4 inch shank.
This also means that if you need switches, you can go to the Tower Hobbies website, look for Futaba Switches, and those five or so replacmenent switches will fit and work as they should. They are the same switch as currently exists in the DX7.
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