Brad, they appear that they are all 7* tapers. The K727, K781 and K783 all match tapers after checking a 7* reamer taper against a spindle and lower control arm taper that I have sitting in the garage.

FWIW, the K5108 and K6024, bolt in GM style ball joints also have 7* of taper. Using either of these and a creative body mounting method would allow the use of GM style tubular upper control arms.

Check Speedway Motors as you can sort through their ball joint catalog by taper, material, height, thread, etc.