Performance mods and interchangeable parts

Hello there,
I am new to Volvo's and I am getting a Volve 240 and was wondering what the maximum horsepower can be by optimizing that engine without turbo or supercharger or engine swap. I like to do an old school project of upping the horsepower. For example I used to have an old Audi gasoline car and there were lots of interchangeable parts like a cam shaft from a diesel that worked just fine in the gasoline car...idled like crap but had lots of power. I am looking for option like that or any other performance mods that can be done to that car to increase horsepower. Does someone know any or knows a site that provides this kind of information? I have 2 x 240 to choose from either a 242 or 245.