Pegasus bit?
I’m not familiar with the Peggie installation in the Fokker at all though I would assume that, forward of the firewall, it is much the same as any other Pegasus powered aircraft of the time.
However, the excavated part looks a little too lightweight for anything to do with an engine installation. It could possibly be the shutter from an oil-cooler duct but, I would reckon more likely, just part of an air ventilation system from the aircraft.
All pure conjecture, I must add.
Anon.