Hi Steve .. I’ve not had a good look at rd forks .. but had a look at the fiche … Couldn’t see a drain plug on the bottom .. so you may well have to take them out .. could be a good time to put new bushes and seals in … As for the preload .. I used 25mm diameter pipe .. it it’s 2.5mm thick wall … I need a 65mm spacer the get it how I wanted … Which was 30mm of sag with me sat on the bike with my gear on . Hope that helps