The original fork matches the frame and is a 1984 model. Trek seems to have said it's 531 dB main tubes, and 531 forks and stays. Many people doubt these statements by Trek, but I'd expect it's 4020 or 531. I have no idea if Reynolds actually butted any fork blades.
This fork was already reshaped once to add trail. This builder is not interested in adding offset back in, because he says it will reduce the stability of the bike. I think now that the first change was a very bad idea, and want to go in the other direction. The current high-trail design is more stable with no front load and skinny tires, but it's not good at all with a 10 to 15# front load. Design with 72 to 73 degrees head angle with 55 to 60 mm offset has been a well accepted front geometry for bikes carrying moderate front loads, such as the Boxdog Pelican, Velo-Orange production Randonneur, a custom design I have some knowledge of, and several of the current and vintage bikes reviewed by Jan Heine over the years. I think my target is reasonable.
As-new it had an offset of 52 mm per the Vintage Trek site, and I'd like to get it near 60, for a trail in the 40 to 45 degree range. After the first re-shape it has about 47 mm offset. So I'd want to restore the original offset (which was good for OEM 27x1 1/8 Panaracer tires without much fender clearance), then increase offset by another 5 to 8 mm. The effective fork length should shorten by at least 2 mm (see the illustrated 44 to 60 mm adjustment example in Matchak's paper), and a more likely value of 5 to 10 mm. The correct length change depends on the exact shape after bending, so I don't believe we can predict it exactly. I'm not that picky about the beauty of the new bend, but I do want the job done neatly
After this bend I would expect to use 700x25's with fenders. I currently use 700x32 Paselas, and with fenders they are a tight fit. The frame's lateral clearances really aren't set up for this much tire and fender. With the new setup I'd be using wheels with 4 or 5 mm less radius than the 32 Paselas. They measure 348 mm radius, and my 700x28 UltraGatorskins measure more like 340. I'm willing to go with smaller wheels to enjoy better front bag handling. Don't take this to mean I'm planning on 650s, however!
If as ClemY suggests 12 to 13 mm adjustments are as much as can be expected, that would get the new rake in line with the '80 through '83 Trek 610 forks, which were offset 55 mm, not 52. Even this change would be beneficial to me, from a rando-bag point of view, though short of the target.
Have I scared you all away?