The CB400 super four I have acquired as a project has Ohlins on the back. The model appears to be HO2360, which appear similar to the newer HO142. I sent Ohlins an email and got no reply so wondered if anyone here knew what spring preload I should set.

I think that the most important thing is the weight of the bike and the weight of the rider. For this reason the preload of the suspension and especially the rear shocks are different for every rider, doesn't matter if you have Showa, Ohlins or Bitubo on your motorcycle. Take a look here.This article is for dirt bikes and we have street bikes but the theory is the same.
http://www.shocktherapyracing.com/motor ... ttings.htm