Here are pics that I hope explain it. First pic shows where the original tank has an area that is angled at 45 degrees for clearance. You can cee the Kirkham tank does not have this, and this area interfered with one of the frame tubes, but just barely.
Second pic shows tank installed- I had it powdercoated black.
Last pic shows the spacer that the Kirkhams made that raises the tank enough to avoid the interference and still has good hood clearance.
