Why two track gauge's on the D4?

Welcome to the BB Moobi. Around here, some farmers preferred the narrow 6U over a wide 7U because they could squeeze between the trees easier/closer, also in narrow rows of grapes, they wouldn't get tangled in the vines as easy, even with the "sweeps" that some installed to keep from tearing up their vineyard. There was a shortage of wide machines here at one time, and some had their machines made into wide gauge machines because they said they did not slip on turns as easily as a narrow. Wide were more popular IMO.
Any pictures of your machine to share? We LIKE photos. JM

Thank you JM.
I thought that may be the case - reflecting the crop rows and possiby a natural evolution from earlier tractor gauges...
Yes, I'm putting together a few photos and a bit on my machine. It was sold new in Australia and stayed with the same owner for 70 years. I'll include photos of the tools, manuals and the grease pump that came with it. I'm a few days away from putting that together but am on it. Thankfully it's not been modified and is running well!

Send pics of her "as is" unless your tractor is bashful! No need for glamour photos hahaha. Sounds like you did very well by getting all of the goodies with it. That's always a plus. Occasionally I get a few tools by searching the toolbox or under the seat; if I buy some more tractors, I may have the full tool set eventually. JM