Hi Welcome to HBZ.
I belive fitment is an issue with those engine, they are to wide and you would have to work the sidewalls...If it has been done, you can find out by searching a little, use various key words and something will pop up.
Cost:well everyone's swap has a different price, this is depending on your abilitie to work on car..you save lots by doing most things yourself, if not it could get expensive.
Rear end:Most commun swap is the R200 VLSD from the infinity Q45, search under drivetrain, everything is covered on that one..Some members are running high hp Z's without a problem.
Kits:I don't know this one.
I have a LS2 Z and drive it to work 3 days a week and on weekends, I have 6k miles in about 6 months, There has been small issues but you can use it as a daily driver.
All models from 70 to 78 are good candidates for any swap, If you start with a 240 or 260 make sure you stiff up the frame a little.if you start with a 280 you can get away with a little over 400 whp with just upgrading the regular stuff.
Craigslist,local newspaper,ebay are a major source.
280Z's are stronger and heavier than 240Z's...
Good luck!