golf gti brake upgrade :)

purchased a full setup (front calipers + carriers and rear + carriers ) of ebay for a bargain £110! next question . front calipers are identical just carriers so need :

312mm disc
new pads
bolt on go

rear .....
286mm .. so are the calipers the same or different? do I need to use the gti calipers or can I use my audi ones .

ill assume its 286 mm disc (only 2mm smaller than my current front WTF)
new pads
carrier bolt on


or do I need the caliper also ?

thanks in advance chris