either mod the 1200 mount or get an engine mount from an 1980something 1200 ute. there are pics on this site showing the engine mounts, just search. radiator upgrade you may want to consider especially for long highways drives and city traffic. a gemini radiator is a popular conversion. search again - lots of pics.
brakes u already have disc front maybee upgrade to stanza struts/120Y castor rods for improved braking/handling/tire size. u can use your 4 speed box with an A15 with no changes to gearbox mounts.
im currently in the process of preparing to put in an A15 into my coupe too.