OEM dampers work in both directions but predominantly in rebound. They do actually control compression a small amount but their main function is to prevent oscillation or 'pogo-ing'. I took a knackered one to bits to see how they worked & reckon that some would be rebuildable, in which case a heavier weight oil springs to mind
The standard OEM Innocenti & Serveta dampers are far better than they are given credit for. Dave Webster used them extremely successfully which, IMHO is great testament. Of the alternatives, Bitobo aftermarket dampers intended for Vijay are highly prized & also were utilised with great success by another race champion, Charlie Edmonds.
The worst front ends I have ever tried (other than badly set anti-dive) are no dampers @ all closely followed by the Kawasaki type steering dampers.....
I'm just saying
but perhaps with a sidecar things may be completely different. I wonder if Serveta might be worth a try, but the forks & links are somewhat specific.
If this response has put you in a quandary, I apologise, but I found the Kwak type unbelievably dire, though I suppose I have had to be a bit of a 'chassis man' having fell off so many times
I have no idea of the practicality, but I could lend you a set of bare Serveta forks, links & dampers I'm otherwise hoarding......