I just did this last fall on my 3400 (same rear as 3000) and I almost feel like there wasn't any linkage specifically attached to the draft/flow control lever. If I remember right, when you move the lever up/down aren't you just adjusting the position of a cam that another component of the linkage (cam follower pin?) hits against? Maybe I'm remembering this all wrong, but it's worth going over the parts diagrams.
Tips:
One of the filters (left side as you sit on the machine) is metal mesh attached to a metal tube, and it is extremely expensive to replace. I didn't see any need to replace that and so I just made sure it was very clean before I put it back (it is literally 100% metal so there is nothing to wear out). I gather that most people do the same. You have to have the PTO shaft out to get this filter out in order to clean it properly, as it sits right against the base of the housing.
I had a leaky brake/clutch pedal seal. The way my loader was designed (standard 730 loader) I had to remove the loader (or split the tractor) to remove the clutch shaft to fix this. I decided to split the tractor which also made cleaning and getting the filter out easier. Removing the fender bolts was harder than splitting the tractor. So, if you have a leaky brake/clutch pedal shaft seal now is the time to fix that.
There were some o-rings that I needed that the kit didn't have, so I would recommend buying a good o-ring general purpose kit before you start this. People say that the unload valve o-ring is not included in the normal sets and that it is important to get that part specifically from NH, as it is an oddball o-ring. I can confirm from experience that this wasn't in my o-ring kit, and did not have an exact match in any of my o-ring sets so I was glad I ordered it separately.
To get one or two of the valves out you will want a slide hammer with an adapter for the appropriate thread (or weld your own onto something), I think you end up wanting 3/8" fine if I remember right. This is the part in the manual where it says you need "special ford tool x" and you really just need a slide hammer. If you don't have that, get a long bolt and a bunch of washers/spacers and you can make it work with that.
When you adjust the linkage read what they are saying in the service manual very, very carefully and you can understand how to do it correctly (which means no trial and error in re-assemblying everything) without their special tools. I literally read this part 5-10 times. Once you figure it out you'll realize all you need is a small depth gauge that you can make out of a small piece of metal/plastic and a file. If the measurement seems way off and you find yourself saying "I can't adjust the linkage that much" then you are measuring off the wrong spot like a lot of us have done, just read it more or ask here and you'll get it right.
I have only worked on this one machine for myself, so take everything I'm saying with a grain of salt. I could be remembering something wrong and describing it slightly incorrectly so if something I have told you doesn't line up with your situation, double check me on it.
