Car firm and corporation from the East ... (7)
I believe the answer is:
hardtop
'car' is the definition.
(hardtop is a kind of car)
'firm and corporation from the east' is the wordplay.
'firm' becomes 'hard' ('hard' can be similar in meaning to 'firm').
'and' means one lot of letters go next to another.
'corporation' becomes 'pot' ('pot' can be a synonym of 'corporation').
'from the east' says the letters should be written backwards.
'pot' back-to-front is 'top'.
'hard'+'top'='HARDTOP'
(Other definitions for hardtop that I've seen before include "Rigid-roofed vehicle" , "Car with a rigid top" , "Style of car" , "Type of car with removable roof" , "Car's rigid roof" .)