The correct tiller is one that covers your tire tracks.
That's the elegant solution, doing it right. Looking professional. Needed if you are hiring your work for others. Or want to take pride in your garden.
He sounds like he just wants to tear it up once. (I expect he will later want to till in his soil amendments, too). Leaving tire tracks over tilled ground, to clean up later with his walk-behind tiller, should meet his needs. He might even be able to mount the tiller offset and not leave tire tracks at all.
I agree his tractor can run a tiller as wide as its tires. That's exactly what it was sold for in Japan.
Here's my Yanmar RS1400 tiller (1400mm, 55 inches) on my 24 hp YM240, the US version of the YM2000 that this tiller was explicitly intended for. When I got it home I made a short trial run, shallow, at 540 rpm then 1000 rpm. (It's designed for an even faster PTO, probably only for a final pass).
And the RS1400 tiller, 55 inches, on my 18 hp YM186D. The US version of YM1510. The little guy is really grunting to turn the tiller if it hits a step-up and has to climb from full depth onto un-tilled ground when cross-tilling. This compact rig fits under my orchard trees better.
Note I hadn't yet learned here in this picture, that the trainer wheels need the axle mounts on the outer side of the wheels. I had mounted the wheel assemblies smooth side out, to not gouge my trees. After swapping sides the wheels don't make ruts.