Need guidance

I have my 1975 280 z, 4 Spd,  lt seen a great life!,  girls, racing, Cruzing, bought in 1983, never quit on me, it has been setting 10 years, 

been reading it on,, This is what I want to do! I guess, drop in a Neo rbdett25 “Nissan”, want to stay in the Nissan engine, Stay true to the car,

try to get automatic engine because the oil pan and avoid the AWD, 
My question is the Rb , 5 spd, trans will match the hole in inside the 280 z.

Or what 5 spd, will work inside a 280z, will a 240sx work? Or 6 Spd ?. From where would get a 6 spd,

Thank you,

3 triples