2+2's didn't start being made till atleast 74, but thats really a non issue lol
you use the engine and gearbox out of the car of your choice, and generally get a custom drive shaft made up to mate up to your diff, although people like to upgrade the rear drive shafts to ones that use cv's, and if you look around on hybridz.org there is info there on putting the s13 or r32 or something...complete rear susspension into 240z's, there is also lots of info on both swaps on there. as far as i know there isn't an sr powered s30 in australia yet?
time wise i'd assume the same amount of time as putting in complete after market gauges, exhaust, brakes, fmic, ecu if ur using pre made mounts so there isn't the time spent working out the right side for them. getting it all perfect is sure to take you forever though, and depends if your going to get it engineered as they might be fussy
rb26 is obviously better and an ls7 would also be nice...
coilovers are generally made by local susspension shops as there are no "off the shelf" type ones cheap, but please tell if you find some
you can get the period style body kits easily enough, suppliers in america are possibly the easiest for modern looking side skirts, which i think look quite ugly on 240z's unless done right
sleep time