The old Shimano retainer ball headsets (HP-6400 and similar) had a stack height of around 32 mm so if you can find one NOS that should work. The newer Shimano cartridge bearing headsets (HP-6500, etc.) had stack heights of about 37 mm so they won't work for you.

I never did understand why Trek cut their steerers to exactly match the stack heights of the particular headset they used with no slack for any replacements. My '92 1420 was made that way too and I had trouble finding a replacement that fit. The HP-6400 worked but, when it finally failed, I "upgraded" to a new fork with a longer steerer to let me use more readily available headsets.