In the picture below you can see the lower arrow pointing to the datum line. The upper arrow points to the dimensions from the datum line up to the locations indicated. I am using the CTS lower rail as a starting point that will coincide with the bottom of the 49 frame. Both are the lowest points. You can see that location "L" is the lowest point of the CTS rail. 4 1/2" up from the datum line. Again this is NOT ride height. This is the height from the frame machine up once the car is clamped and gages are set. I want about 5 1/2" ride height in front with the suspension in its sweet spot, so I will drop the temporary angle iron clamped to the frame 1" rather than leave it as is and subtract 1" from each dimension. Too easy to make a mistake changing dimensions on the fly.
Dimensions "C" and "G" are the locations for the front and rear cradle mounting bolts. Notice that these two lines are tagged. There are the normal height dimension; 11 1/4" front and 10 1/4" rear. These are the dimensions from the head of the bolt with the cradle installed. Follow that line upward and see the tagged dimensions; 13 7/16 front and 12 3/8" rear. These are the dimensions I'll be using. They are taken with the cradle removed.
I have moved the angle iron down 1" so it now represents ride height.
If you follow lines C and G up to the overhead view you can get the bolt locations from the center line of the car. 16 1/4" in front, 16 1/8" in back. Double those to get the width between the two bolt centers.
I cut two pieces of 3 x 5 x 3/16 rectangular tube to 24" long.I went up to 3/16" wall because of the step that only leaves 4" of height in the front half. It doesn't hurt to over engineer a little. I cut the 1 1/16" step in front and cut a radiused pie slice in the back to bring that surface downward.
I'm going to sink some 1 3/4" x 1/8 wall round tube into the frame to shore up the cradle mounting points. I measured everything out and notched the frame rails to accept the round tube.
Here's the rest of the hardware for the mounts. These are NOT washers. I used a hole saw to make these out of 3/16" plate and welded the metric nuts to the back side of the plates.
All pre assembled. I'll double check everything then weld them up.