The important measurement is the height above and distance from the plough point, one of our ploughmen will know the answer.

You are quite right- there is a series of spacers on the bar which normally rust together. The easiest way to free them off is to dismantle as much as you can (take the disc off and it’s arm at least) then put the whole assembly into the middle of a very hot bonfire; I use a 45 gallon drum filled with pallet wood. At the end of the fire you should be able to pull it all apart.
The centre spindle that it all assembles onto is round bar with two flats machined on it- this leaves some large gaps down which soil packs hard, jamming the spacers on and encouraging rust to form. That’s why you have to get it all red hot to dry it out and convert the rust back into powder; it should come apart then, providing you’ve got it hot enough!
When ploughing I tend to find that the critical distance is between the tip of the ploughshare and the bottom of the disc. Normally three fingers is the gap, but so long as the disc bearing isn’t bulldozing the topsoil on the left hand side and there is some sort of gap between the disc and the share for stones to pass through then anything is correct.
Your width should be set to 9″ or 10″ and depth of work about 6″ or 7″; so long as you have the plough set around there you should then be able to set the disc about 1″ to the left of the share.
Obviously it all depends on soil type, compaction, etc., which is why different people keep winning the ploughing matches. It is more of an art than a science!

The width setting is the one on the top of the headstock. To measure how wide you are ploughing you put the plough in the ground and pull it forward to achieve it’s normal running depth. If you stand at the back of the machine and look at the landslide (or the main beam) it should be vertical- if not, adjust the angle on the two bolts that attach the plough to the drawbar. The holes are slotted so should slide easily around the tapered mandrel in the middle.
Once you know that the plough is vertical, pull it forward until it seems to settle down again then you can take your measurements.
The width is measured from the face of the disc to the vertical face of the previous furrow (the one that the right hand wheel should be in). I usually set mine to between 9″ and 10″ by turning the transverse screw on the top of the headstock. I also try to set the disc about 1/2″ to the left of the plough point by adjusting on the disc mounting slide.
The only other adjustment is the depth which you adjust on the long screw that sticks out of the back; it needs to be about 6″ to 7″ measured from the top of the vertical cut to the bottom of the furrow.
You can then adjust the disc height to suit the conditions, but I usually run with all the spacers under the slide (at very most I take one spacer out and put it above the slide); at this it usually puts the disc bearing just clear of the soil. On no account let the bearing housing for the disc bulldoze the soil because it will pick up sand and wear it out.
I hope that helps!