OP here. If it's of any interest, I've now done loads of them, generally reuse the old bolts and do them up by feel with a longish combination spanner.
What are you feeling for? Not a facetious question, I just tend to use the FT setting as suggested by Steptoe. Also often use the old bolts and have never had a problem.
EDIT for aircon flared fittings we use the crowfoot spanner adapter at right angles to the torque wrench and no correction factor - although, in most cases, we just use the FT setting again.