The plow share grabs the soil and sucks itself down as far as the lift will let it. Yes, if you hold down on that hydraulic lever and allow the 3pt to drop all the way, you will be left spinning your wheels. However, if you lower the plow until it touches the ground, then start moving, the plow will plow efficiently with minimum slip (there is ALWAYS some minimal slip, even though it won't seem like it). You'll just have to keep your hand on the hyd lever and regulate the plow depth yourself, because you don't have draft control (Another Ford advantage) 
But, personally, if it were me, I'd put the rockshaft and the original plow back on. After all, that plow was tailored to the B, and they work extremely well. The 3pt design was not intended for a B, and I'll tell you why, comparing the B system to the tractor that was made for 3pt work....(Shameless, you guessed it!) Lol! 

Don't want to talk bad about the little Allis' (as I have a B), but for plowing with a small plow (1-3 bottom) on a 3pt hitch, the Fords really are superior. (And the WD's and WD-45s are superior to the Ford, in my opinion. SC is just a better design. Saying this from a non-biased point of view, as I really am an Allis guy in every respect, except for this one little thing...the 3pt). The way the hydraulics work on the N's and Jubilees are far superior to a B or C in my opinion, because unlike the N series which have hydraulic levers similar to modern tractors, (You can position the lever anywhere on the quadrant and the plow will raise or drop to the set level, and you can set a stop if need be), with the Allis, whenever you release the handle, it pops back to the "neutral" position. Unless you put a stop on the remote cylinder(s) then, it makes it hard to stop at the exact same point every time, and you must have your hand on the lever the whole time you are raising or lowering, because the lift will stop whenever you let go. 

Also, the fact that the draft control works extremely well on the Fords (provided they have been adjusted a couple times over the last 60 years). With the Ford, you achieve your draft control by how low you move the hyd lever. For example, when plowing, just drop the plow until it barely sits on the ground (No further, unless you weight the tractor). After setting the plow down, set your stop under the lever. That way you don't have to think about it whenever you want to drop the plow again after you turn around- just go down until you hit the stop! Can't do that with an Allis until you get into the WD/WD45 and D-series (except for the D10/D12) 
After setting the plow down and setting your stop, just go! By just setting the plow on the ground, you've set the minimum draft load. This means when the linkage senses a stronger pull (which leads to slippage), the tractor will just barely bump the plow up a hair to keep you going without slippage. Of course, you can set the draft lever lower, and all the way down cancels out the draft control for the most part, and that will ultimately stall the tractor because the plow will bury itself as deep as it will go. 

However, if you set the plow down then push the lever down another inch or half-inch, the draft lift function will be delayed some. In other words, it will take a harder pull to bump the plow out. So...when you start plowing, the plow will suck down and your wheels will start to slip excessively. To compensate this, the lift will bump out a large amount, and the tractor will lurch forward, then the plows burys itself again, making the wheels slip again. Then the draft control will bump the plow out, making the tractor lurch forward. This is not only hard on the tractor, but hard on the operator. I made this mistake when I first got my 8N and didn't have a clue how to correctly operate the draft control (which are most people who hate Fords, from my experience). Because I didn't know how to use it (even though I thought I did) it set me on the path to not liking this tractor too much. In fact, after those first couple bad experiences, I quit using it to plow with and only used the B and my Oliver 2-12. (I still really like that rig!) Then later I found a nice YouTube video explaining how to use the draft function, and a light bulb went off! I tried it the way I mentioned at the beginning of this post, and it's been the greatest plowing rig! I really do like it. After all, the N's were plowing tractors to start with.

Whew! This is longer than I thought it'd be! Sorry! (Let the Ford hate messages rain down, Lol)