Since it is going to be cut down anyway.............recommend that you first cut square with a chainsaw each part of the two separate trunks about 1 foot above the "V" notch. After you have dropped these two, examine the cut ends for the amount of heartwood diameter exposed, and carefully note the growth rings, the finer they are the better. This presents you with a decision point as to whether you want to pursue rifle stock(s) or firewood above the "V" notch!! If you have more or less 8-10 inches in diameter of heartwood showing (doubtful), next cut off a 4-foot mini-log and examine the amount of heartwood diameter at that smaller end...and so on until there does not appear to be enough heartwood to fashion the butt stock area and fore arm rise of a rifle stock?
For your "V" notched stump, dig it out with the backhoe. Clean it up so that you don't mind using your chain saw on it to trim away the roots!? Kind of trim the roots off to match the diameter of the trunk exposed above ground. Take it back to the barn, and really clean the underground portion up. Locate a good "band saw" mill operation. Carry your trunk to the mill. From your picture, I can't tell you what you've got? Since the most valuable part of a lower walnut trunk like you have just cut up is the under ground portion (for veneer), first ask the mill operator, "How much is it worth?
Then, if you still want to pursue rifle stock(s), ask his advise in cutting it up? I would want to be present for that cutting, and put in my 2 cents worth (since I majored in Forestry in college). I would be inclined to first have him exploratory cut straight down the "V" to produce equal sides. Next, rotate one of the halves to "flat side down" on the carriage, and start cutting 4-inch wide planks...same for the other half. And, if you have not abandoned the "4-foot mini-logs" from atop the "V"; start cutting 4-inch wide planks.
Assuming that you've really got some GOOD rough-cut wood here...and the mill operator thinks so too; it's time to think about "drying" the wood. The cheapest method is to air-dry at your place...someone mentioned in the attic. If you have "hay barn" space with concrete floor, that's great! Your garage, covered back porch, etc. Mind you now, for uncontrolled "air-drying", we are looking at 15 to 20 years. Hopefully you will have a level concrete floor. "Level" is key here, if you want to have nice straight 3 and 1/2 thick planks (shrunk, didn't they) in 20 years, you must start stacking your planks from a "level foundation". Proceed to Home Depot and purchase some of their finished red oak...we want to use this to make what is called "stickers" to separate the stacked planks to allow air circulation. For your 4-foot planks, I'd recommend (5) 2-inch wide stickers crosswise under each plank, starting on the concrete, with stickers directly under each other as they proceed up the stack. I don't know how high we are getting here!!? So, maybe you might need 2 side by side stacks? Cap each stack with your worst plank, and put your old 250 pounds of bar bell weights across the top to keep them straight. As someone mentioned wax the ends...I've used the black tar that horticulturist paste over cut tree limbs to protect the wound...to forestall checking and splitting on the ends.
Just sit back and wait. The worst think that can happen is that you might just have some well dried fire wood down the way! I did it with a 32-inch diameter small end, wild cherry 12-foot butt log about 19 years ago! Haven't come up with a single stock yet, a lot of other things like fireplace mantels...but it just cost me $60 bucks to have it band sawed up.
Good luck!
Dan
