If the 15x7 wheels take a 3" trim ring, they will not work with a 15x6 wheel.
Normal trim rings used to be available from aftermarket/universal sources. Generally with a "Chevy" look to them. Much less expensive, too, with the aftermarket gripper retention method.
Typically, the trim ring has a gap of about 3/8-1/2 inch between it and the wheel's center area.
You might look around on eBay and such to look for the "Chrysler-like" ridges and such. "Brushed" can be added with 600 grit red Scotchbrite and such, I suspect.
CBODY67
