Not sure what to do

Nothing is wrong with my current engine, its a bone stock 318 from 1974. i want to get more power without spending too much money. would it be smarter to put better parts on my current engine or swap it out? i assume the engine has over 120k miles, the odometer broke before i bought it.

Would cylinder heads with bigger valves and a performance cam be worth the trouble or should i save my money and buy a short block crate engine? thanks for any thoughts and ideas. i want to have fun with the car but it seems to be a money pit when it comes to making it handle and have power
just to respond to everyone, the engine already has a four barrel carb and intake and im planning on saving my money and buying a 360 magnum crate motor, even though it will break the trans and rear end but **** it