Hi,
You are over thinking this. First, if you are making some sort of English fowler, I recommend the upper trigger guard with the smaller bow. That is much more correct in size and shape. Second, that bow has 3 tabs for the anchoring pins and two lumps of sprue that need removing completely. Keep the forward tab under the front of the bow as high as you can so the hole for the pin will be hidden inside the lock mortise on the lock side. The other two tabs can be 3/8" - 1/2" tall above the inside of the trigger guard. I do not recommend using any pins smaller than 1/16" and I do not like 1/16" either. A 1/16" drill breaks really easy when you are drilling the holes and pins that small don't have a lot of strength. A lot of guys use 1/16" pins but I prefer 5/64" and on musket sized guns, I use 3/32" pins. If you are making an English style gun, I suggest looking at my multi-part tutorial on just that topic in our Tutorial section. It is under "Miscellaneous Tutorials".
dave