The race is on for the PGA Tour's rank-and-file with only six weeks of tournaments remaining to qualify for the FedEx Cup Playoffs. This week's Rocket Mortgage Classic presents a great opportunity for the field, with only one top-20 player making the trip to Detroit. The grind is on for those trying to earn — or keep — their spots in the playoffs and trying to get into the top 50 in the world for next year's signature events. Our golf experts preview the event starting Thursday at Detroit Golf Club, and provide their favorite prop picks along with best bets to win this week. ROCKET MORTGAGE CLASSIC Location: Detroit, June 27-30 Course: Detroit Golf Club, North Course (Par 72, 7,370 Yards) Purse: $9.2M (Winner: $1.65M) Defending Champion: Rickie Fowler FedEx Cup Le…