Dan has reccommended replacing pipes

Fizz

to improve heating quality of 4 radiators attached to same branch.  I've had sevral contractors come to do it and they have suggested other options as they feel the proposed pipe replacement too complex.  One has suggested re-piping lateral B to another main section(see scheme); the other has suggested repiping B to dropdown off main(see picture).  The dropdown was the result of an add-on to system back in the 30's, and supplies 2 rads of 118 edr.  Added edr would be 36.  Which would work better?