We don't have monoliths anyway.
I did come across this interesting read tho if anyone is interested about our own solar system.
solar system Saturn's moon Titan Here is what I think, and why I think Titan would be better than Venus.Although Venus would be ideal, I don't think that you could move Venus without disrupting the delicate balance of the other inner planets, IE: the Earth, Mercury and Mars. But you could destroy IO, take all or parts of IO, use the asteroid belt and make a planet big enough for what you are wanting. Plus you already have a heated core and atmosphere with Titan.
Besides, I am not sure if I understand the whole planetary engine dealie. You can't just stick some thrusters on a planet and move it. The planet still rotates, so unless you stop the planetary rotation (very bad) your thrusters are going to move the planet all over the place.