i was installing the hps1000 on my 68 and i mounted the bottom to the car but when i went to tighten the top nut on the threaded shaft, the shaft rotates, i am sure it is very simple but how do i tight the top nut?

grab ahold of the shaft, not the blue dust boot, with a vise grip plier. not too tight with the vise as you only need to tighten to 12-15.

The top of the shaft should have an indentation in it for an allen wrench.

If your shocks do not have an Allen head like Tom mentioned (many do not, but I don't know about the Bilsteins), you can go to an auto parts store and get a shock absorber tool (mine is Lisle brand, but I have seen others). Like this: http://www.toolfetch.com/Category--Automotive--Suspension_Steering--Tie_Rod_Ball_Joint--LIS20400.shtml

One of the two smaller parts will fit over the oblong end of the shaft, and the hollow piece fits over it onto the nuts. Two wrenches, and you have tight shocks.

Bilsteins have an allen head recess in the top of the shaft. It's metric.

Bilsteins have an allen head recess in the top of the shaft. It's metric.

Yes. I just put these in my 77

The Bilsteins for my 01 Silverado didn't have the Allen socket, so I needed my tool.

im not sure about the bilstein's but some shocks i have seen have two flat spots on the sides of the shaft. So you could get an adjustable wrench on it to hold it from spinning.