coilovers
I have both Strange and QA1 double adjustables. 3000# backhalf BBC car.
I like the Strange better, plus they rebuild their own shocks and struts. QA1 do not rebuild their own at their factory. They will refer you to one of their dealers. When I talked to QA1 at the NMCA race at Indy this year, they said it was too expensive to their customers to do their own rebuilds. It cost $150+ for them to do it and customers complained that was too high.
Double adjustable gives you more tuning options. If you can sell the sinlge adjustables and get doubles, I would do it. If you can't get rid of them, just find the quickest consistant 60' that doesn't get you in trouble at the big end.