Reviews on the Timevalve are a bit mixed, although the general consensus seems to be that (1) it is a good system and (2) it is a bit louder than stock.
My stainless steel system was made in Germany and is the basic staple installed by Van Dijk here in the Netherlands. It costs around $750 front-to-back. The connection to the manifolds requires standard steel bolts with copper nuts that are self-locking. If the fit is correct, then this connection should be very tight. With my previous system, I could never get this connection tight, no matter what I tried. This was due to an improper fit. I installed my new system myself, working only with jack stands (no lift) and it was pretty easy. You do need to take care to route the system right, observing the necessary clearances. Using the right size donuts and other installation hardware is important. Although the standard installation is to weld the sections together, I am happy I used clamps - this way the fit can always be adjusted until just right and the system can be removed easily should this ever be necessary. I neglected to use installation 'paste' and have some very slight leaks at one or two of the joints, but this is negligable. I will correct this *sometime*.
So, in short, you should be able to install a good-quality system (Timevalve or Borla or ??) yourself in maybe two hours.
Cees Klumper in Amsterdam
'69 white 280 SL automatic