I work on a lot of these. Just about every ambulance is a Ford diesel.
What you have to do is take the air box off. Loosen the clamp on the "elephant trunk" intake tube on the driver's side valve cover. Loosen the clamp to the silly resonator box and yank out the elephant trunk. Take a large hammer and a block of 2"x2" wood and smash the sh!t out of the stupid resonator box. It is the easiest way to remove it, and it makes your future repairs a *lot* easier. On the elephant trunk, you can use a spray can lid or a bearing cap to seal the hole in the side of the tube.
You now have good view of the fuel filter bowl. The filter bowl is held in place by 3 13mm bolts that go through the HPOP reservoir, and also 4 fuel lines (for the 99-03 vans) and maybe a couple more if it is a 95-97 van.
If you are only going to change filters, it helps to bend the engine wiring harness to the left a little bit to make more room in there. One thing that will help you immensely is to get a fuel filter that is 2 pieces. Truck filters and some "van" filters have a filter permanently mounted onto the cap. They are hell to install in these vans. You can find other brands that have a cap separate. Mush easier to install. There is just enough room to slip the filter in, then the cap.
Once you get the fuel bowl off, I recommend replacing *every* oring on there, since you have it off in your hand anyway. It would be a shame to have to come back to do it again for lack of a 3 cent oring. Check out
Replacement O-rings for Diesel Engines
They have kits that come with everything you need.
Back to the HPOP. Once you get the bowl off, you will also have to disconnect the Exhaust back pressure sensor. Unplug it, then unscrew it from the sensor line. Then unscrew the line from the timing cover access port. Then remove the timing cover access port. That gives you the access you need to get the HPOP gear bolt out. You also need a quick disconnect tool for the oil lines (99-03) or a wrench to remove them (95-97). A "Performance Tool" brand hydraulic clutch disconnect tool works pretty well. To get the drive gear bolt out, a 3/8" impact wrench does pretty well. I have one that barely fits between the radiator and the timing cover with a regular socket. Then it is 2 10mm bolts under the back side of the pump that hold it to the cover.
Oh, one thing I forgot. Remove the fill plug in the top of the HPOP reservoir and suction as much oil out as you can. There will be a little over a quart in there. It makes the job cleaner when you finally get the pump off. Make sure you also remove the Injection Pressure Regulator electrical connection before you pull the pump out. It is on the back side of the pump.
There are really no special secrets about working on vans. It is just how ever you can do it. The only thing I have to offer is that you don't need the resonator box thingy. And that when you put the elephant trunk back in, tighten the clamp just enough to stay on the plastic joint on the driver's side valve cover. You can put it back in and it will stay on it's own till you get the air box reinstalled. When the engine is running, the suction from the turbo will keep it firmly in place. It make future maintenance much easier.
Good luck, and welcome to the 'Org