go with an aftermarket steering shaft. Id go with the MM solid steering shaft assembly. Its quite an upgrade over stock. "Other aftermarket steering shaft assemblies have their U-joints secured to the steering shaft with small
setscrews. These setscrews protrude out from the
U-joints. It is not unusual for the end of a setscrew to
hit a tube of an aftermarket header.... The MM Engineering Team designed a new steering shaft that does not use setscrews. That’s right, no
setscrews! Instead, we secure the U-joints by
welding them to the shafts. We attach the steering
shaft assembly to the steering rack with a pinch-bolt,
just like Ford did with the stock steering shaft assembly.
An added bonus with the MM Steering Shaft
is the addition of a telescoping center portion to the
assembly. This collapsible section eases installation,
improves fitment with aftermarket k-members,
and improves safety in the event of an accident."
79-93 Mustang Steering Shaft Assembly For Power Steering Rack by Maximum Motorsports at LRS - Same Day Shipping!
http://media.latemodelrestoration.com/downloads/instructions/MMST-11r2.pdf