I have a friend who converted a 1983 610, and could not fit 42's. On my 1984 610 I can fit 700x31 (actual) with fenders, but I think it would be quite tight with 35's.
Mine is low trail (64 mm offset) based on a custom fork, giving about 36 mm trail. Jan might say it's too low but I like it (for 700c he recommended something like 40 mm as a preferred value). I do not think 50 mm trail or 46 mm is low trail. Mine will handle a Berthoud bag with a decent sized rear bag, pretty well.
One interesting about these Treks is that the 73/73 combination of angles, the 42 to 45 chainstays, and less-than-7 cm BB drop make the geo very similar to his beloved Herse (or was it the Singer?).
But in general there's no way I'd consider the original 55 mm (pre 1984) or 52 mm (1984) forks to provide low trail. My original 52 mm fork certainly did not feel like it, either.