Best would be to cut off the front triangle and build a new one as you'll never get brass brazed lugs apart without destroying some pieces and/or totally nuking the head tube. But, are worksman frames brazed? I thought they were all tig/mig.
On a welded frame, you could grind the old down tube welds off, do the tube extensions on the top tubes, and put in an entirely new down tube, better for safety and easier since it will be meeting the headtube at a different angle than the old one.