I've upgraded the original 34-year-old Boges with the Adjustable Koni (internal rod, not the dial racer set) with the stock springs repainted. They are an amazing upgrade. I'm just finishing the rear bushings this week. The 'weissach" bush just became available to the aftermarket after years of being NLA. At a minimum, any new shock/strut upgrade from what you probably have will make a HUGE difference. If I was running a more "stock" car I would suggest just going with the BOGE or whatever Roger/your supplier of choice recommends. I've got a lightly modified 86.5, and the adjustable will allow for some change to ride (not going to race it) over time as they soften up. They are also rebuildable. Check the other forums and the opinions are as varied as "what oil should I use", but there are fewer choices. Boge, Koni, Bilsetien, Oliens, in that order by price. If you're just wanting a decent ride go with the Boge or Koni's. There is about a $300 difference.
If the springs are good you can clean them up and re-use them. I just read you can have them re-hardened (didn't know that) but I'd doubt that would be necessary, but others may have better insight on this. I do know a few people that warned off of going too crazy on a street car with spring swaps and specifically to stay away from progressive rate springs. Hope that helps.
