Many thanks to all those that have responded. I got called away to do something last night and I have been busy at work this morning so I have been unable to view the responses until now.
I understand all that has been said about using the holes to achieve height adjustment. However, even with the height pins in the bottom holes, I believe that the implement will be sloping forward, quite severely.
There are two circular adjusters. Above each wheel. You can see one of them quite clearly in the pictures I have taken. You cannot really see the other one as, currently, it is set as its highest level and is below the level of the main framework. These are attached directly to the wheel mounting and simply raise and lower the height of the wheels/the main structure.
The adjusters that can be clearly seen also raise and lower but, if I am honest, I cannot recollect what, specifically, they raise and lower. I believe it is the main framework too, so forming an additional level of adjustment.
We have an outdoor horse arena. The soil is not sandy by any stretch of the imagination and appears to be what was left after the previous owners simply scalped off the grass. As it dries out, it harrows relatively well with a quad and a chain harrow but SWMBO is always asking for something with "more bite" to get a little deeper.
Our current neighbours have stated that this was the implement that the previous owners used to use. There were "reiners" and used to perform the sliding stops etc., that such riders do. I can only assume that they would need a "loose" surface to be able to do that. They had a much bigger tractor than we have and I would estimate that it was likely to be at least 60 hp, but I honestly don't know.
They left it dug into the ground in its current location and the duck feet were probably set for a depth of 2-3 inches or so before I began to adjust it.
Our intention is to be able to use it to loosen the surface of the arena and, depending upon how large the clumps are after we have done so, perform some form of additional harrowing to get the pieces to the size we want.
There are very heavy chains attached to the back of it (you can see them in the photos) and it would appear that the previous owners attached a chain harrow to this implement.
I would guess that the implement is about 6 feet wide and, when looking at the ducks feet from the rear, it would appear they would tear up across the entire width inside the tires (there are 3 rows of them).
I will have another play with it once the wet weather stops (rain is forecast for the next week or so) and will report back how things went.
Once again, many thanks for the advice:thumbsup: