Did you ever figure out your chains sizing and how did you install them ( what size spacers)
Just getting into this on same tractor
I have both F & R 2 link ladder chains for my B3350.
My 3350 has the standard sized R4 tires. Tire chains require wheel spacers, and I have the Kubota 1 3/8" spacers on my 3350. Tire chains CANNOT be installed with the optional, oversized R4 or R14T tires.
I bought my chains new and, as always, it was necessary to fit the chains to my tires. In my case it was necessary to remove side links from both F and R chains and to remove a cross chain (2?) from the rear set to achieve proper fit. It was also necessary to add a cross chain to the front set. Expecting a new set of tire chains, which are designed to be useable with multiple sizes of tires, to fit without modification is unreasonable.
I do not have measurements handy but after a couple of hours of fiddling was able to fit both sets properly such that they can be installed without tools (aside from a set of channel locks), fit tightly and do not move without any need of tensioners, or other band aids. It takes a bit of time to install tightly but there is no need to remove air, etc.
FWIW: I have an extra new, unused set of front chains to fit standrd sized R4 tires for B2650/3350, LX tractors and other tractors with the same sized front tires. Price is right but shipping will kill most deals.
To the OP, I expect that you will be able to adapt the chains that you now have to your 2650. The best way to do so is simply attempt installation and modify as necessary. Tirechains.com sells cross chains in various sizes if you find that you need such
SDT