The top link is going to be wherever it ends up with the plow turning properly. I think leonz is right on the length of the top link, but as beenthere points out, don't get too hung up on top link position side to side.
I set up my MF 62 (2 bottom 12 inch) according to an
OLD Ferguson manual (see link below).
Ferguson Moldboard Plow Service Manual
It'll take some patience, but the manual is printable, once you get the hang of how to do it. I had to load each page then print them, then assemble into a book. There might even be a manual for your plow in the same website.
Anyway, I initially set mine up with the cross beam set as the book recommends, and angled down slightly for better suck. I found jacking the tractor up to my intended plowing depth (6 inches) didn't work for me. According to the Good Book, the plow should sit level once you have the tractor right wheels down in the furrow from the last pass. If you don't, the shares will plow different depths. The first pass is "setting the stage" for the actual plowing job, you'll need a deeper draft setting on that one since there IS no furrow for the right wheels.
Once the first pass is done, park the tractor with right side wheels in the furrow and eyeball the plow for level crosswise and fore and aft. It should be slightly nose down IMO, and level from side to side. The nose down keeps the coulters cutting well, and helps draw it in quickly. Mine's at full depth within the length of the plow.
I set it up so the landsides were parallel with the tractor frame at first, it would plow ok but not flip the sods completely over. Tweaking it a bit nose-left cured that, as did turning sharp left at the end of each pass. If you didn't do that, the whole sod would want to roll back over as soon as you lifted the plow. Mind you, I was plowing soil that hadn't been turned in 30 years, so the sod was pretty thick and tough.
You need a place to practice. I ended up with a bigger garden than I planned on because a few passes were wasted on set-up. The moldboards should be shiny-smooth and free of paint, otherwise it won't scour properly (sticking mud). Anywhere the ground touches needs to be bare metal.
Left and right adjustment isn't critical in my opinion as long as you have the front plow taking a full bite. If the setup of the crossbeam is right you'll have that happening. They base the left-right offset numbers in the manual on a given tractor width inside the tires, and a given gap between the 3ph arms and the tires. If yours is wider or narrower, you'll have to adjust accordingly.
Once the first pass is done, park in the furrow with the inside of the right front wheel just about touching the vertical edge of the first furrow. If you have lots of shale or sharp rock, you may want to give a little more clearance to avoid cutting tire sidewalls. Then drop the plow and measure the distance from the front landside to the edge of the vertical furrow wall. You want to be just about 16 inches in your case, or slightly less. If it's more than that, the front plow won't completely turn the sod over because the bottom "keel" at the furrow sole is unbroken. If it's too much less than 16" the two furrows won't be even. An inch or so isn't a big deal.
Plowing speed makes a difference in my experience. Too slow and the sod doesn't "flip", too fast and you tend to lose any precision.
I'm new to this as well, but some of the folks I work with are "old pros" when it comes to plowing, and there's a lot of good info to be had if you ask the right people. What worked for me might not work for you, but plow setup is an almost lost art, as one of the guys I work with says. I had more fun plowing a couple of gardens this fall than I've had in a long time, when it's working well a plow is a pleasure to watch work.
The 3400 must be somewhere close to the tractor size the Ferguson manual uses as a baseline, because I didn't have to tweak too much. I know the wheel to wheel width was close. Ideally, you'll have the insides of the right side tires perfectly lined up. Mine isn't like that, the rears are wider stance than the fronts, but it didn't give me any problems. Really wide rear tires aren't good, a good plowing tractor will have the front and rear tire fitting neatly into the last furrow. A 16 inch plow shouldn't be a problem with a 4700 in that respect. A 12 would be minimal.
Good luck and keep us posted, questions are good and pictures are better...
Sean
