[Reggie677]

I have a 77 nova, I want to put a new trans and motor in my 77. I want the hp and torque, but don’t know how big of a motor I can put in my car, before I make that decision. I don’t wanna lose my air and heat in my car either.

 

[62 NovaWagon]

Welcome to Team Nova!

Easiest and cheapest is a 383, if you have a small block now it's just a bolt it, if you're gonna travel 700R for the overdrive, easy install.

 

[Elvis]

Even easier and cheaper, the tried and true 350/350 combo.
SBC 350 bolted to a TH350.
3.42's in the rear end and she will, as the old song used to say, really get lost!.

Nice thing about the '68-'79 Nova's, the engine bay is large enough to fit anything.
From a 153 four cylinder to a 632 big block, there's plenty of room.

However, you say you want the HP & Torque, but those terms are relative.
What are you starting off with?
A fresh 350 4-bbl/350 combo I mentioned, compared to a worn 305 2-bbl and Metric 200, will make the car seem like a rocket ship.
However, if you're already starting off with a modified engine/drivetrain, then you're obviously looking for even more power.
So what do you have right now and what kind of "improvements" are you looking for in a drivetrain, and maybe we can help you better.