42RH in 68 Dart advice/request

FWIW, I did mine without the “special” tools, just a $28 amazon digital caliper.
The round bar is 5.5. “, and the caliper extends enough to down to where yo need, you just need to be careful to measure to the right “landing” and subtract 5.5 inches from the reading to get to what the chart is calling for.
For the 2nd measurement,
The flat slotted bar is .5” thick. A guy on utube used 1/4” plate, I used a piece of .620 square tube. You just have to be certain it is straight. He had to add .25 to compensate to get what the chart was looking for, I had to subtract .120.