neilnevill, that mod is to get 170mm on a standard U-Turn on the cheap.
OP – I’ve had a re-think and it cannot be done with a non u-turn spring, the rebound damper has around 175mm of travel which means that there is 5mm of play due to the spring not being fixed to the shaft unlike a u-turn. There must be something different in the rebound / MC side of the non u-turn models.
You can test this by undoing the u-turn spring at the bottom, pull the lowers and you gain the extra travel.