I was looking at those some time back. Had the same problem you have. Current designs overlapped with my tractor but old styles wouldn't work.
Curtis has changed their newer cabs design to fit a broader range -- that is they are less specific now. In the older models, the cab to fit the
B7300 also fit the
B2410. The
B2710 and
B2910 are both larger overall than the
B2410. The 1KB2710 model was specific to the
B2710 and
B2910.
If you could find the old model numbers 1KB1700AS or 1KB1700SS they would fit your
B7300. The 2710 model is too big for your tractor.
Here's info on the old models/styles that you mentioned and what other tractors you could cross-reference from.
1KB1700AS fits
Kubota B-1700, B-2100, B-2400, B-2410,
B-7300, B-7500 (Hard Sided Deluxe)
1KB1700SS fits
Kubota B-1700, B-2100, B-2400, B-2410,
B-7300, B-7500 (Soft Sided Deluxe)
1KB2710AS fits
Kubota B-2710, B-2910 (Hard Sided Deluxe)
1KB2710SS fits
Kubota B-2710, B-2910 (Soft Sided Deluxe)