Yeah, I have the same question, along with a few other members. Progressive Suspension doesn't give any guidance in their instructions, other than see service manual. I did call them, but they took a message and said they will get back to me. That was two weeks ago and with the current crisis, I wouldn't expect to hear back anytime soon. I think it's fair to say the air gap is somewhere between 110mm and 140mm....lol.
