the water pump will physically fit, though i have noticed the a12 uses a different blade design, and as to the difference in performance i am unsure

when your doing your cooling system there is a couple of different temprature thermostats available, i always go for the lower 76 odd degrees one instead of the 86 odd degrees one (just a random point that popped into my head)

gemini radiator is good, i think i used a 91mdl excel top hose for this and stock 1200 bottom hose

the extractors should work as unfam said you may need to grind inlet a tiny bit if using stock manifold (but i would bank on em fitting)

you may need to tweak your engine mounts for the a15, check my photo gallery for "mounting block diagram" making two of these plates (possibly weld them to your existing mounts or just bolt on) is a simple way to get around it