You could, in theory at least, use the old forks with the new arc. They are just held in place with a single screw on each side but I've never tried to do this. Is your old arc broken?
As for the Jade... they are growing on me after the mods. They are still abnormally forward which and have weird tonality which is probably due to the membrane and I don't want to swap that out. The midrange is very nice though there is something that's bothering me. I can't quite put my finger on it but there appears to be a mild texture on all voices. The bass is more subdued and better controlled but more like the Lambdas then the Omegas.
I could try to damp the drivers somewhat but the less times I open up the housing the better as the lead wires on the drivers could break and that would be a PITA to fix...