I fabricated race cars for years. First, find the factory frame bracket. Check with the common 4 speed vendors such as Passon Performance or Brewer's Performance. They should be able to get you headed in the right direction. They might even be able to provide you with some demensions.

Otherwise, you just have to make sure that the z-bar is square in the car relative to the centerline of the ball studs. Generally speaking, it will be perpendicular to the crankshaft centerline and be square and level as viewed from horizontal and vertical.

Tack it in place and assemble the linkage. Check it for binding. If it's action is clean you're good. If it binds, you missed something. Check to see that the z-bar is installed correctly (not backwards, etc.), you have the correct linkage rods and that you are square.

These linkage set-ups are not high tolerance instruments and they don't have to be =/- .001". they have a bit of "give" in them but if you get it in there square, you should be good.