My 1st question would be what their manufacturing capabilities are; that would refine or set expectations for possible products.
I would think they'd want to work on items with a higher volume first, or maybe those where the market supports a higher return on investment.
They might want to pick Tony D'Agostino's brain - also Joe Suchy & Jim Kramer, if possible - for items they get requests for but can't supply.
Lots of things come to mind:
Air Grabber ducting
The notorious thumbwheel dash-light dimmer switches
Proper/correct brushed trim rings
Recall wheels
Decent fuel sending units
Lower dash pads for '68-'69 B bodies
LA-engine left side manifold heat shields