Sorry.. I was thinking about the pallets used for freight.. my bad.
On a side-note. Transmile (Malaysia) used to have seat pallets for the convertible 737-200. I remember visiting their aircraft probably in 1995 back in the old Kuala Lumpur airport (now a regional commuter hub-SZB) and I believed at the time they actually used freight pallets as a base.
One thing that struck me was the condition of the overhead lockers... they were in horrible condition due to fact that the warehouse guys not building pallets to the correct contour which resulted in the pallet scraping the bins as they moved aft.. Transmile has QC as well as pure freighters at the time and looks like the warehouse guys really did care which one was operating!
Anil