103 RM = F1 with Foam tires, still selling in KWS
103 LM = Leman, wider chassis 底版, Leman body
103 GT = use touring car tires, different 底版 and bumper
103 RS = similiar to 103 RM, with F1 narrow 底版, rubber tire, Leman body (eg, Toyota GT-ONE TS020) and BLACK PIG Motor
They are the same with many share parts. Download the manuals from Tamiya and u will know.