If you are comparing strictly on horsepower alone, 47 horsepower puts you into much newer Kubotas like the Grand L4740 or maybe an MX4740. For the Ford 830 at 40 horsepower, the L3600 with about 39 hp comes to mind.
The truth is though, looking at a L4740 and a Ford 3000 - aside from the seat and tires and horsepower rating, they do represent tractor technology that is 30-35 years apart. The comparison is not fair. Both the 3000 and the 860 are well before Kubota's time in North America.
The Ford 3000 had a 10 year run from the mid 1960s through to mid 1970s - the Ford 830 was even before that. At that time, Kubota had very little to offer in their lineup and nothing in that size - period. The most Kubota you could get in 1975 would be the L285 with about 30 horsepower. In 1984 Kubota started to fill out their L Series lineup starting first with the L4150 at 50 hp.
Like Eric says - a bit of an apples/oranges comparison, but if I had to pick, I would say the L4150 for the Ford 3000 and the L3600 for the Ford 860 - largely based on approximate vintage and horsepower range. It has only been since the mid-to-late 1990s that we have seen Kubota produce 50+ hp equipment in larger volume.