I was going to get a BH77 as well. The dealership was going to deliver the tractor without it (and did) and do a separate contract at the same finance rates 0-0-60 for the hoe. Had no idea when the subframe would be available, and Kubota wouldn't lock in a date. So I bought the tractor without it, and they said they'd come and get the tractor when the subframe finally came in, and deliver it back to me, no charge. That's a pretty good deal. But, the more I used my tractor around here, the more I realized a BH77 would have a finite use cycle for me, and I'd wind up with a very expensive piece of equipment sitting in a corner collecting dust and dry-rotting. The BH77 is nearly $10K and I had no way to justify spending that kind of money for it other than some stumps that I could get out earlier if I had it. Termites and wood rot will get a stump eventually, for free. As wet as it is here, a stump won't last long.
So, no, your situation is NOT unique. The LX has enough design changes in the frame and assembly that the B series sub frames do not fit. So if someone tells you that your LX is a just a B, they're wrong. You're not going to be able to go out and grab a B subframe and bolt it up to your tractor. But I'm sure you already know this by now. You might be able to get your dealer to do the same deal mine offered. Go ahead and get the tractor now, and get the hoe when the subframe comes. At the very least, the dealer/Kubota should agree that it's the right thing for them to do to pick up and deliver the tractor for the installation, or comp the installation for the inconvenience of you having to transport the tractor. That way, at least you'll have the LX to play with until your hoe comes in.