I recently completed install of the components I ordered from Derek Speare Designs, and I am very pleased with the quality and performance. I purchased:
Track Boss button box
G25 / G27 Wheel Adapter
Pocket Plate for Sparco P310mm Wheel and SLI-Pro
Derek, I would say that your dimensions for the wheel pocket plate are spot-on. Button spacing, SLI-Pro match-up, pocket depth wiring clearance, and back cover dimensioning are faultless.
To accomodate the two SLI-Pro rotary encoders I drilled two shaft holes equidistant from the two closest button holes and the raised wheel hub platform outline on the inside of the pocket. The spacing was correct to fit the encoder body inside the pocket with clearance for the other buttons and the raised wheel hub platform outline. Once installed, I used a dremel tool to trim the encoder shaft lengths.
The HDPE material qualities of the pocket plate make it very easy to work with. Drilling, trimming, and modifications are easily accomplished with standard tools, the material seems durable, and the plastic has natural noise damping qualities. Plus, the HDPE naturally holds the button mounting nuts in place, acting as a natural lock washer.
The SLI-Pro is a fabulous tool! The rotary encoders are a must-have feature. The right knob switches the right alphanumeric display between RPM, Elapsed Lap Time, Previous Lap Time, Best Lap Time, Running Interval vs Best Lap, among others. The left knob selects Speed, Oil Temp, Water Temp, Lap, Position, Individual Tire Temps, and others. In short, it displays all of the data otherwise featured in the HUD / MoTec.
Great Stuff, Derek