What 88mmNotch said. I am using Victor Jrs as well. The 1 5/8 headers should have more than enough material on the flange to port out to match your head. I am running 1 7/8 primary on my Victor Jrs. so you should have plenty to port out the header flange. Only issue is that you may need to reweld the header if port threw the weld. If worried about porting threw the welds then port the flange meeting the head and port at about a 45 degree angle to if nothing else help funnel the flow.Any room to port out the flange a bit?