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!