Best advice, don't do an engine swap if you're on a tight budget. A 1977 will be a 280z not a ZX. I'd highly recommend you spend time searching on upgrading/replacing stock parts on your. Make the car reliable, a stock Z will be blast for a learning autocross car, when you get used to driving it stock or slightly upgraded and you have some money saved up, then look into upgrading your engine. Start small and don't get caught up into the engine swap if you're going to have to cut corners on the build.
Welcome to the board and USE THE SEARCH FUNCTION, it will make you stay here much easier on you and everyone else.
Tyson