The SS seat unit has a very thick base and then there is loads of padding so just putting a replacement seat unit on (like a fibreglass race seat) and a thin layer of seat foam means you lose about 3-4 inches in seat height!
We did the same on all the race bikes we built - put some kind of box under the seat unit to raise the level - but we used a much lighter and advanced composite material to make our boxes ... wood!!
