Stan,
I agree figuring out if your specs are correct is the most important thing. That I had done at a reputable pro shop in my area. The thing they cannot offer is the Ultimate Thumb mold process I use at Buddies. Switch grips are fine but if the locking system wears out from use, you are back to square one on getting the right feel in a thumb hole, if you are like me and need the hole to feel just right.
You are totally wrong if you think that hitting the lines is that easy for pro shops. I have been to many and depending on how busy they are, being exact does not always happen. So, I'm not going to give you a break!!!