Steering wheel vibration

86 944 ls3 swap. Prior to the swap I noticed a vibration while driving came in around 40 and then would start to shake the steering wheel bad as I accelerated. I figured tires where old and when I would do the swap the wheels and tires would be replaced.
So this is where Iam now. Swap is complete and still have the vibration..
This is what has been done. New wheels and tires I road forced the wheel twice to make sure rebuilt rack new inner and outer tie rod ends, new steering shaft factory control arm bushings and ball joints, new struts and strut mounts alignment is good did that again today. I own a shop so I have everything at my disposal. The Strang thing is I can drive down the road and it may be fine then I true around and start to accelerate it comes back in I have to say its pretty bad. Also I have replaced the wheel bearings and races and turned the rotors on my lathe. The hubs are in great shape I have ran a straight edge across them prior to turning the rotors the rotors cut perfect and you can see them as they are being cut how they look.
I have not done a rotor run out with them on the car figured since they cut well they should be good.
I have even tried other wheels still the same. The rack is from 944 online I know Ian well new rack clamps and bushings as well on it. To me it seems to be all centralized in the steering column itself. Steering column is tight. What am I missing here??? Thanks in advance for any help I have hit a wall with this. The other thing I have been thinking about is how does the steering shaft still line up to the notched spots on the rack and column when the cradle has been lowered 1/2?

Your description sounds like the classic out of balance condition....especially because it starts at 40 mph.

However, when you said you "road forced the wheel twice to make sure" perhaps you were referring to a dynamic wheel balance on the vehicle.

Either way, I think you need to determine if the vibration is purely speed related and not dependent on engine rpm.  

While coasting at 40+MPH, the source of vibration felt in the steering wheel, is either an out of balance tire, a bent rim, pulsing brakes or steering rack issues.  It seems you have eliminated the tires and wheels if they were balanced.  The reconditioned rotors should eliminate the brakes.  Rims in good shape?  Are you sure the rack is secure?  

A friend brought a car to me with steering issues that included play and vibration at speed.  Turns out the rack was coming loose from the chassis!

BTW, are you using a hydro boost for power steering?  It may be an irregular pressure issue pulsing the rack mechanism.  Just guessing here, I'm not that familiar with HB function.  i know they have to be filled properly and the fluid must be worked in by turning the rack stop to stop multiple times. 

Regarding the steering shaft compatibility with the rack and steering column, 1/2 inch spacers on the cradle do not prevent the factory connection.  It mostly changes the angle of the steering shaft and not the length.

Keep us posted!