Seems to me they had to go down quite a ways (not sure it was two feet though) because the old trolly tracks were still in the pavement under who knows how many layers of asphalt. They dug up the original brick pavers too.
Don't know how much they lowered the roadbed, but Metro North raised the bridge by putting at least another 6" of bearing blocks under the beams. (That on top of a previously installed raising block of who knows what vintage..)
Another interesting tidbit is that even though that section has been single tracked for whoknows how long now and thus the second span is no longer used, when they raised the bridge they raised both the active and unused spans (instead of removing the unused span for scrap.) Tends to indicate they have an idea that they may need to relay that second track at some future date. Probably after the Portageville Bridge is rebuilt.. ;-)
(That info for any Ferroequinology buffs out there. ;-)