I am currently restoring an NSM1 which arrived de-rigged.

Rather than using a lever, the mast ram is operated via a wheel at the deck end of the shaft which acts on an internal thread to add or reduce pressure to the back of the mast.

The wheel has an external groove to take a rope and there are holes in the deck immediately below the wheel for the rope to pass through.

What I can’t work out is how to rig the ram so that the wheel can be turned from the back of the boat. The rope has to be under continuous tension to turn the wheel.

Can someone help me please?

I had a mast screw on an old smokers i had which also came in bits. There is a couple of options. One is to use a Continuous length of rope which is what i did or you could use just on control line leading aft with a strong peice of elastic attached to the oter end and fixed at the bottom. The threads on the screw are quite large and so you do not need much movement.
Your best option though is to scrap it and nivest in a ram or strut. Thats what i ended up doing!!

Ram photos...

'Mighty Screws' or thats what they called them, they suffered from friction badly, to work effectivly you need as you have figured to keep the line pretty tight is not easy. Some tried to run the line down under the deck then across the boat side to side so the crew could adjust it! not pretty.  The simplest & most effective idea I saw was a 3" diameter trolley tyre fitted over the screw to make it easy to adjust by hand, giving up on the string.  Better & simpler solutions made the device obsolite. levers work far better.