The only time we had a bit of a moment for an empty positioning flight on our BMA DC-9-15 was if the forward air stairs had been removed for MX. (They weighed 150 kgs)
We had to chuck in a couple of MG tyres in the forward hold to keep the CG in trim for the load sheet and/or have someone on the FD jump-seat for the ride.
Went like a rocket on take off