I know I've badgered you into more and more photos, but I/we haven't yet seen the condition of the shares. A plow won't go in the ground if the shares are worn. I took a plow out once to do 'just a few acres'. It had worked fine the previous fall, but now it didn't want to stay in the ground. I finally bit the bullet, went to town, and got new shares. Night and day difference! the plow practically 'jumped' into the ground.
One disadvantage of a mounted plow is that it hasn't much weight to aid penetration. You may need to attach some ballast on the back. There are also 'Deep Suck' shares available.
As to the lever, it's called the Landing Lever, and it's for adjusting the width of cut for the front bottom. Should have zero effect on penetration of the rear bottom.
At this point- and really before you even went to the field the first time- you should follow instructions in the Operator's Manual for initial settings, not rely on what worked for the PO. You can look at it for free on-line
here.