ahhh, Rome wasn't built in a day, sounds like you have a full plate going on.
If you have someone that can help you out with the welding part, your idea about making a longer scarifer to use in your BB sounds like it would work. Just be careful not to get too deep all at once and bend it. You could even drill a few holes into the side of your BB and bolt one scarifer to the side panel but a lot lower than it is now and be careful and go slow, not too deep, and scratch out a good ditch. Then clean it out with a shovel. You could even bolt a piece of good strong 1/4" thick tubing to the side of your BB and buy a "shovel" type plow to bolt on to the tubing to clean out the loose dirt after you run the scarifer through it. No, it wouldn't be as heavy or strong as a potato plow but a lot cheaper and using your BB to mount it to the tractor. Use it for what it is, with care, and you can get it done that way too. Sure would beat using a hand shovel.