IMO - Just dont get too hung up on the measurement stuff.
Whether you run a 6.9 60 or a 6.4 60 doesnt mean anything if you dont know how to play the game - or do not have a feel for the game.
The measurement stuff - in many cases - have become an excuse for laziness. The easy way out - and the safe way.
If you can run 6.5 - and dont know how to steal a base - you will be out most of the time.
If you can throw 90MPH - and dont know how to pitch - you will get hammered.
If you can hit 450 foot bombs with an aluminum bat - but dont know how to hit with wood - you will be pursuing your next career sooner rather than later.
I would spend most of my time watching instincts - and desire - and going from there. Thats the hard part.
I wouldnt spend much time on the measurement stuff. Even people with poor vision can tell whether a kid has a strong arm - or is fast. You dont need a SPARQ rating or a stopwatch for that.
Good luck to you and your son!