Hi Dennis
The book states to suit lights & as I do not as yet have them, I decided to err on the side of caution
Much easier to cut a small amount off rather than try to add a piece in.
I made the oval tube & cut it to 120mm
Having an offcut of 47mm od pipe this was used
I ended up with an overall length of 167mm
Having fitted the front roadwheels 15" X 195 & turning lock to lock, plenty of clearance for a 6" or 7" headlamp unit.
I hope this is of some help to you