The fuel tanks are pressurized thats what the line that goes to the muffler does so it will likely still work. Sometimes its impossible to get the fuel lines above the the needle valve So you just get it as close as you can and don't sweat it. That said an inch seems like a lot and he should have been able to get it closer than that by using a different size/ shape of tank or drilling the fuel lines in another location (regardless of what the plans say). Even if it doesn't work its any easy fix.