I have used them, heims, on trailing arms (toe in rods) on IRS cars replacing the stamped steel trash with 1" od 3/16" wall DOM steel tubes.
Those use 3/4" left and right threaded tubes. That is as small as I would go on anything. That is the sizing needed to replace the bolts provided by the car manufacturer. That's on little 4 bangers with skinny tires and intended for everyday street driving in an economy car.
How does someone come up with using 1/2" for competition? Put away your slide rule and use your common sense?
They will stay tight for about 500 miles then they start to rattle.
You could use the Jeep style that are intended for vehicle suspensions but have rubber inserts instead of Teflon.
My opinion of course which on the Pantera is don't bother. There is nothing to be gained, only lost.
"We" found a company that actually made nice extruded tubing arms for this application. All nice powder coated black, threaded and knurled. They failed withing 20 miles.
The company bad-mouthed my solution only to have their arms fail by pulling out the heims and bending the arms.
Mine are ugly but they are still going, albeit with rattles?
You need to KNOW exactly what you are doing with this stuff. If you are dead, you won't get as much fun out of driving your car? I have other plans. Everyone is free whatever they choose?
You have to know where to stop modifying the car. Heims are over the limit.
Detomaso started as a race car builder really. He/they know how to build a suspension.
As Bosswrench has mentioned, it is very difficult to improve upon the stock suspension arms on this car.
Likely they will be heavier and they certainly will not have the proven durability of the stock arms.
The aluminum billet arms are actually heavier and their durability is questionable.