Saturday’s Chevrolet Sports Car Classic at Detroit’s Belle Isle is set to feature a 32-car field, in the first Prototype and GT Daytona-only race in the TUDOR United SportsCar Championship.

There’s been a few changes since the initial entry list was released two weeks ago, including confirmation of Patrick Dempsey’s substitute and a late driver change at GB Autosport.

With Dempsey and co-team principal Joe Foster in Le Mans for Sunday’s official test day, the Atlanta-based team has drafted in Brett Sandberg to team with Andrew Davis in the No. 27 Porsche 911 GT America this weekend.

Sandberg, a regular in the Continental Tire SportsCar Challenge, will make his TUDOR Championship debut as the team’s designated Silver-rated driver.

GB Autosport, meanwhile, has made a late change to its lineup, as a business commitment has forced team principal Michael Avenatti out of the cockpit for the second consecutive race.

Porsche Supercup driver Ben Barker will instead team with Damien Faulkner in the Tully’s Coffee-sponsored Porsche, in what will mark the 22-year-old British driver’s U.S. racing debut.

TBAs are still listed for the No. 19 Muehlner Motorsports Porsche as well as the No. 64 Scuderia Corsa Ferrari, which could bring the field down to a 30-car entry should both withdraw.

The Prototype class, meanwhile, still features an 11-car grid, including five P2 cars and the return of Olivier Pla to the wheel of the No. 42 OAK Racing Morgan-Nissan.

No Balance of Performance changes have been made to the P class cars since the last round at Mazda Raceway Laguna Seca, although the GTD-class Aston Martin Vantage has been given a 1.0 mm larger air restrictor, as well as a ride height adjustment for this race.

Additionally, the size of the refueling restrictors have been adjusted for the Porsche, Audi, BMW and SRT Viper.

Practice gets underway on Friday, with qualifying later that afternoon and the 100-minute sprint race taking the green flag Saturday at 12:10 p.m. ET.