As I understand it, the rules for entry to the meeting wouldn't allow it. However, please bear in mind the Magnette is a road car, not a race car and was built with low key competition on mind.
One of the reasons I didn't enter the Hulme with the Marcos is the performance and size difference between my car and others. When I visualise large 500bhp+ metal bodied cars in HMC, sharing the track with my 90bhp at the wheels tiny fibeglass car, or racing against Tony Roberts 700bhp Corvette in the Sports GT race, then sorry, I see potential problems.
Ditto with the Magnette you run amongst cars of a similar performance and putting a fairly standard 190bhp Rover engined car against 500bhp monsters is not on.