[7.62x39]

Have you drilled the holes for the TG screws yet?

How much are you missing by?

I would definitely use a backing plate, not so much because of the TG, but because of the mag release.
There is a fair amount of load on it, changing mags etc.

 

[7.62x39]

Maybe you could split the distance between the trunnion holes and the TG holes.
Moving each half the distance, you need to make up.

Max