OK made some measurements, some of which Cagey provided.
All measurements were made on headstocks with a 1 11/16 nut and Schaller tuners, so 6 mm posts.
These measurements are the Inside to Inside post measurements for the D - G string.
Vortex - 45/64 17.76mm
PRS - 41/64 16.27mm
Possible with the 3x3 tuners I have on hand - 27/64 10.84mm
Desired for straight string pull - 19/64 7.72mm
So if straight string is desired in a 3x3, you will have to offset them.
If you think the PRS layout is close enough, realize it gets you 47% of the way there.
The Vortex gets you 47% of the way there.
Possible with the 3x3 tuners I have on hand with a totally custom cut and drill (starts at $125) gets you 71% of the way there.
But wait, that is just the distances Inside post to Inside post, lets look at it from angles from the nut.
After all its the angle we are interested in.
I used 113.48 mm from nut edge to center line of D - G tuner posts. That is a measurement I made on the PRS. Visual inspection shows the Vortex is quite close to the same.
The angles are:
Vortex - 85.53 *
PRS - 85.9*
Possible - 87.27*
Desired - 90*
Those resulting %s on how close to a straight string pull are:
Vortex - 95.0%
PRS - 95.4%
Possible - 97.0%
Desired 100.0%
So if the PRS layout is close enough to you, the Vortex is only 0.4% off.
The best you could every hope to accomplish with a symmetrical 3x3 is only a 2% improvement on the Vortex with a typical 3x3 tuner. Are there non std tuners you could use to achieve it, sure. (Is that worth $125plus extra and your design efforts when you are already practically there?)
Mods - feel free to sticky this.