RE: Mathews Question?
If you have a good shop they should verify that the draw length is correct anyway. That being said it may not be exactly the same as the bow you have. Mathews is not known for having exact specs. They tend to be high on draw weight when the limbs are bottomed out and the draw lengths tend to run longer than what they are rated at as well. Like if the cam says 29 inches don't be shocked if the actually draw length is closer to 29 3/4.
Also if both of these are used bows there could be string stretch issues which would effect the draw length as well.
Adding a loop or shooting off the string does not change the actual measured draw length of the bow, but it will effect the perceived draw length because your release will be farther back. Using a longer release will do the same thing. And an over draw does not effect your draw length either, it just puts your rest farther back so you can shoot shorter arrows to get less weight. Not really needed anymore considering the speeds of newer bows and the lightness of carbon arrows. They are a bit harder to shoot though because it makes your bow less forgiving. Most of the drop away and full containment rests have some sort of overdraw to them.
You should really put this question in the archery section, either the bowhunting or technical. You will probably get more responses, and possibly from someone that actually sells and works on them.
Paul