86.Rx-7.MADNESS

I guess my engine on my 86 seven is gone cuz it throws water from the radiator cap, plus white smoke comes out from the rear so i guess its gone, do u think i should buy another engine or should i just buy an 87 that theyre selling to me for about 600 bucks? plus if anyone could let me know what would be the first things to do to my car if i buy the 87 so it can run clean, and later on i would like to buy performance parts, would someone be able to help me out with this??????