After some more investigation, yours is early than I thought.
Yours would be a TF with a 4JB1 engine, where what I was thinking is RA with 4JJ1 engine.
If you can reproduce the vibration in neutral, then a two person analysis may find your concern.
At that age, it would be possible the engine mounts have lost their compliance and are starting to act as solid.
I would also see if the vibration is still there with the clutch depressed and in gear, that way the clutch plate and all the gearbox internals are isolated from the engine.
If you do engine mount rubbers and the bracket, make sure everything finds a an equilibrium when doing everything up, including inspecting the transmission mount.
I would also check the exhaust system for and impact damage, that may put stress on the engine/trans mounts.
I hope this may provide some help to you.