Just in case this answers some aspect of the question; the front trigger guard screw on a no1 mk3, and the same on a no4 mk1 etc have different threads. The no 1 is a finer thread. They are very not interchangable without severely damaging something important, the threads in the receiver.
All screws on no1 mk3's have a slight dome to them, and all screws on no4 enfields are distinctly flat across their top, so at a glance you can sort them out from each other.