There are six bolts on modern trads.
The front two go through the chassis crossmember.
The second pair are just through the floorboards and the rear pair, which are longer, go through the double skinned crossmember ahead of the rear wheels.

Here we are. Scroll to the end.
http://www.talkmorgan.com/ubbthreads.php/topics/155291/Seat_height#Post155291


DaveW
'05 Red Roadster S1
'16 Yellow (Not the only) Narrow AR GDI Plus 4