yeh, you could leave the cg box in it,s stock position (and shafts) but i think that means you have to cut into the o/s chassis rail :suspect:
i am not sure you do, the GA is not much bigger than the CG in fact i don't think it is bigger at all. the problem is that people use the existing mount on the drivers side which brings the engine much to close to the chassis leg. on a hard left the engine hits the leg. but with nismo bushes this is minimised. in the actual car i believe the engine mount is much bigger and longer so it keeps the engine away from the chassis. its just alot easier to make a new gearbox mount than a drivers side mount. so if it is lined up with the CG gearbox it should be all good... and would save alot of hassle too.
as for the exhaust, same again, it comes out the front of the engine in the same way the CG does so if its sitting where the CG does then it should all line up.
the only issue is with the cold idle sensor. that is seperate where as on the CG it is all part of the TB, the result is that it doesn't idle properly if its not wired in. but there may be a way to modify the wiring, or i hear Matt Humphris may be working on a way to block off the cold idle valve and fit a needle screw instead. this means that also the GA throttle body can be used on the CG engine.
the radiator is only difficult because on the GA, it has a double width radiator and one hose attaches at one end of the engine and the other at the other end of the engine. with the micra they both attach on the passenger side of the engine. now a stock micra radiator will cope with the GA16 engine, but a pipe needs to be run from the drivers side of the engine over to where the radiator is.
the CG ecu should run the engine too, i think the map is pretty much the same just applied to a bigger output, eg, injectors are bigger but so is the engine and the inlet manifold etc.
but the GA ECU would be better and is a straight fit,
the gearlinkage is a staight fit too i think, but depending on where the gearbox is and what gearbox, you may have a bit of a floppy gear lever or long travel between gears, but then its not too hard to chop down the linkage.
the other point you need to remember is that the speedo is out, so either use the original speedo (straight swap into the micra dials) or get it re calibrated,
also the brakes need to be uprated, but the 1.6 brakes should just bolt on pretty much...
so all in all it is a very easy conversion comparitivly speaking, i really want to do it, very much, i think it is the best convertion you can do, i think 2.0 is too heavy and too powerful for the front wheels, and i think turbo is too complicated or unreliable.
i just need the space and the time and the money...and a donner 1.6 lol
