My current motor has over 200k miles on it. I'd like to swap it out for a motor with lower milage that is original specs or if there's a V6 that is compatible that won't require much else to be swapped or modified.

I've done minimal work on vehicles. Oil changes, brake pad replace, air filter change, thermostat replacement, little things like that. I am ignorant of what kind of work would be involved in going up to a V6 from a 4 cyl, but I am guessing it would involve a new transmission and various small things like the pumps and belts.

Does anyone have experience with a reliable source for a motor with low miles? I would appreciate any help I can get.