PP, As Xfaxman and LD1 have already pointed out the 3tpl is the place where Harry Ferguson designed tractors to pull from for the simple reason that it is the only SAFE place.
I would call 2 feet deep a subsoiler. Terminology varies in different parts of the same country, and even more so in different countries. You have 85hp, so plenty of pulling power. Having done the same as you on several farms around the world - breaking in vrigin ground, I would suggest that you build your framework to be able to take 1, 2 and 3 subsoilers. One behind the centre of each rear wheel and one in the centre of the tractor. I think you will have sufficient height of lift on the 385 to be able to have them at a fixed two feet depth, but you might be able to arrange it also that you can have a variable depth (pins through the carrier and the leg) for transport and then lower them once you are in the field. My NH has limited lift height and this is what I did with my 3 leg subsoiler, also designed to go 2 feet deep. I only have 45 hp.
You could do some trial passes with a single middle leg. Then cover all your ground with the two legs behind the wheels. With two legs you straddle the previous pass so that one wheel is running where the centre line of the tractor was on the previous run across the field. This way you subsoil to the same effect as if you were pulling all 3 legs, although you do run on some subsoiled lines. You do not need to go the full depth on the first pass. Cross subsoil at right angles to this pass, perhaps with all 3 legs on, or just the two depending on your ground conditions. Again you do not need to go full depth. If necessary, make a third pass on the diagonal. This all takes time, but it is cheaper than hiring somebody with a big crawler to do the job for you. Perhaps like me there is nobody with such a machine anyway, so you have to do it yourself.
It is possible you might have to cover all the ground with only one central leg for the first pass. The important thing is not to go too deep with any number of legs so that the tractor is struggling to cope with the force of pulling the legs through the soil. It is better to go shallower first and then cross the land again. You might find you can go full depth with all 3 legs on the first pass, or you might find you can go 1 foot with 3 on the first pass and then 2 feet at right angles.
The speed at which you travel determines how much the soil is broken. Too slow and you simply make a line through the soil. Too fast and you are likely to bust something. To begin with choose a speed you think might be suitable, drive a few yards , get off the tractor and have a look to see what effect you have had on the soil. Nobody can tell you in advance the speed at which you should be travelling.
