I have a 98 Malibu with a 3.1 and I want to put a 3.1 from a 02 Buick Century in my car.
Is this a drop in or do I have to change some things ?

How much power does the 02 3.1 have ?

the power on the 3.1 should be 170hp

I have an motortrend article right here that showes a modified bu' w/ a 3.4 venture ohv -v6 238 hp, so it possable, and the hood isn't modifed so it looks like the 3.4 can fit in.