Adjustable isn't going to happen. I've never seen an adjustable set for sale for any normal car. If you were serious about your handling surely you'd lower it to an acceptable amount then correct the roll center with a fixed RCA, then tweak with other adjustments. The only way i could see an adjustable RCA being made is with a ball joint with a long thread, then a chamfered nut under the hub and a lock nut on top. Youd just completely do away with the taper fitting. The problem you then have is fowling on the CV joint