I'm easily confused - it must be my age
.
From the top of the tombstone to the bottom of the glass : 2-3 mm
On the left: you won't hit any obstructions until you get to the graveyard on the left of the playfield.
On the right: the entire tombstone plastic is above the level of the ramp on the right - so you won't hit anything until you get to the cabinet on the right.
Again, I've assumed you won't be using the black plastic part at the back of the tombstone.
Hope that answers it. Yell if you need more.
Cheers