I've been thinking about making one and I'm going to use a 3-D target to get the size or lines right. I can get an idea of where they go put them on and then move them if needed.

A good idea...in theory...All I know is a mature buck can be anywhere from 180 to 300 lbs on the hoof where I live. That has to transfer into a different chest measurement, say anywhere from 18-22 even 24 inches. I bet that can put you off by up to 5 yards at thirty, ie enough to cause a bad hit or even miss. Under thirty....well most can estimate yardage well enough by themselves at that range. In the deer woods I will stick to my eyes if no rangefinder. The above would force you to estamate the chest size which is no easier than yardage IMO.....