Sturmey 4 speed FW trigger, 3 speed grip shift.

[rjb]

The 4 speed trigger on my Moulton salvaged from a garden feature was very gritty probably due to rust, dirt, debris within. I had a Sram MRX 3 speed front shifter in my spares bin. I rigged up a weight attached to the cables with the trigger on the bench. Using a ruler and pointer attached to the cable I measured the cable pull.
Sturmey 4-3 pulled 10mm, 3-2 pulled 5mm, and 2-1 pulled 8mm
The SRAM MRX had 9 positions and 8 clicks. 3 clicks pulled 10mm, 2 clicks pulled 6mm
Pretty close to the Sturmey if you set it up so you pulled 10mm (3 clicks) to get you from 4 to 3, 6mm to get you from 3 to 2 (2 clicks) and 10mm to get into first (3 clicks). Basically I set it up so the cable was tight in 1st ( bottom )gear
I've been out on a short ride and it works perfectly. Any adjustment can be made on the fly using the cable adjuster on the shifter.
This is how the gears lined up on the gripshift. May have to remark them if it works long term.

[hoogerbooger]

Now I would be feeling dead smug if I had done that. I hope you enjoy the further field testing.