I just found the greatest set of Stirling SMG scratch build templates I've ever seen. They are leagues ahead of the BBC ones and produce an exact 1:1 scale replica. Best of all they don't just rely on you to print the sheets out correctly, they include all the measurements taken from a real Sterling right down to the length and diameter of the cocking handle, as you can see in these preview shots:
These things are so detailed, they also include the full interi