As I read it, they're repairing (and presumably painting) the existing Haverhill deck/through truss bridge. If they do a thorough job, they might get back to the old B&M 35 MPH passenger limit. This won't have a lot of effect on current passenger operations, as MBTA trains stop at Bradford & Haverhill, 0.4 mi. apart. Downeasters might gain a minute, but schedule-writers have to allow time so DEs can hold out of either station when an MBTA train is at the platform.
I don't have an ETT handy, so I don't know the old B&M freight speed. I am less sure that it can be achieved now, with heavier freight cars. But even 10 MPH OR two freights on the bridge simultaneously would help Guilford significantly, with a follow-on improvement to passenger schedule-keeping.
Today there were about 10 pickups at Andover St., one may have been marked Gilbane. I glimpsed what might have been the westerly signal mast upright at I-495. Crews working at both Shawsheen bridges. I-beam piles driven at the Andover bridge, and an excavator repairing the retaining wall down at river level. An excavator drilling a hole for a deep poured concrete column at the LJ bridge.