Glad you started me off on this, been meaning to do something. The regulator has 8 Belleville washers 12.4mm x 6.2mm x 0.7mm. They are stacked in normal series configuration - ()()()(), you can change the pressure by changing the configuration slightly (see link). Should be easy to get a steady 5ft lb, but be careful not to exceed legal limit. I will pm you more info after I have been to the range to chrono different settings.

Regards, Baz

http://springipedia.com/belleville-washers-stacking.asp