ok, if i go down that road will there be any problems with timing or the tune being that the engine might have different specs?

so ive bought a m20b23 engine with and 5 speed manual behind it from a 1985 323i and i want to swap it into a 1990 318i that had a m40b18 with an auto behind it. The engine is in the car and now all i need to figure out is how to wire the engine harness up to the body wiring. any help would be much ...