I think you really have to get the box blade off the back of your tractor before you get bogged down so far you can't lift it enough to detach it.
Take your pickup down to the local wrecking yard and get a big car hood, maybe even the hood from a pickup truck.
If you turn this upside down, it makes a nice sled. Use some fender washers and eye bolts to give yourself two places to grab it. Despite the fact that you can't horse the BB around manually, you can put the hood under it, drop it on the hood and then pull it out of there.
I was just looking at chain, and 100' of 3/8" proofcoil chain will set you back just under $300, and will be quite useful in the future. Between this, the car/truck hood converted to a sled, and your pickup, you should be able to get the box blade dragged out of the way. Set it up with a short length of chain and a removable link to get a "Y" configuration to pull on both sides of the sled at the same time. You will need an additional 10' or so of chain for this to work properly.
Note: you never have to manually move the BB an inch using this technique, and once you have your tractor free, you can just drive over & pick it up again.
Now put a 4' x 8' piece of plywood under your FEL bucket, hook the chain to the rear of the tractor and slowly pull on it with the pickup while using the bucket to crawfish the tractor backwards. You may have to repeat this a few times to get out.
If this doesn't get you out, and you really want to do this yourself, go out there with a second piece of plywood and a shovel. Dig out enough mud to get the second piece of plywood under the back wheels, so you really have something to grab on to and then try again.
Any way you look at it, you will have some nice ruts to repair in the late spring.