CUTFB,
Speaking from in-house experience, I believe a low PG grade will not hurt your son, however a high PG grade will help him. If that makes any sense? I'm not a fan of doing any showcases in the off season, especially if your player is not a true one sport, player who trains year round. Especially a PG showcase which is a grade and a write-up that will live on the web for long time. Son just recently shook a low grade that he had to live with for some time. I never felt it hurt him as coaches 99% of time trust only their eyes, but it sure did not help him!
Consider the June 2018 PG Academic Showcase to improve his score. Or, by looking at his target list of schools (as PABASEBALL recommends above), cut your losses with PG showcases, and do targeted showcases. Those coaches won't care a lick about his 7 on PG.
As far as going as a PO? I think going to the showcase or not as a PO isn't the question at this point. I think the question is, should he be a PO full time, or not? Then do what he is at the PG event. But if he is still playing both ways and training as a two-way player year round (travel and school) ? Then what's there to be afraid of? Must be a two way player for a reason. Showcase it.
But if you're worried his fielding and hitting is pulling his pitching grade down at a PG showcase, then it must also be doing it at other tournaments and outings (school and travel) ? Hope I'm making sense here.
As far as hypothetically attending another PG event where he throws well at 85, 86? As a PO? Yes, you will see a jump on that grade. By at least a full point or even 1.5. As far as running the 60 as a PO? Unless he is a sub 7.0 I wouldn't worry about the 60, and not run it. But if he's 86 from the mound and can run a 6.9 or lower, it can only help by demonstrating athleticism and upside for more potential. If he goes as a 2-way guy he will have to run it. Anything above a 7.2 will not help and begin to be a big negative.
But really, don't worry about the PG grade. My son had a low grade and I NEVER felt it hurt him. Hard to believe, I know. But I swear it didn't. DIDN'T HELP HIM EITHER!! But didn't hurt him......that I am aware of. Not one coach ever mentioned it throughout his recruitment.
Hope this helps.