Around $650 for a full set of rebound adjustable only koni 80 series, can’t found the details now about where to get them I’ll find them latter.

As for installing them, easy on the rear just undo the lower shock mount on the trailing arm, remove the top of the rear seat, take the black plastic covers off  that are just below the parcel shelf, once that’s done you’ll be able to see to the metal caps that the shocks are bolted to, undo the 2 m8 (13mm head) bolts and lift the metal cap and shock absorber out together. Fronts just jack the front up take the wheel off and it’s pretty obvious what to do.
good luck(it's defiantly worth doing)

Hi Colin and Scott,thanks heaps
you both have been very helpful
....long live the 105 coupes...