I just completed a "2 servos-in-stab" set-up on my latest design. I also used 3421s. It concentrates about 87 grams (3 ozs) to the tail, so make sure that your plane can tolerate that much tail weight. Turned out mine did not and I ripped the set-up out for the sake of tail lightness. The photos I have are not descriptive enough unfortunately.

What exactly do you think you need? Maybe I can describe it to you in PMs. Basically I put the servos into sockets cut into the stab. The stab was about 1" thick at it's thick section so the servos fit flush with the surface of the stab. It was a little tricky fishing the wiring back there since I don't have a plug-in stab, but I made it work