What I would do is get some plasticene (or similar) and put some big lumps where the blocks are supposed to be, then fit the seat, with the metal loop sitting at the bottom of the lock and the front spigot (attached to the fuel tank) sitting in its cubby hole in the front of the seat, then measure the thickness of the resulting "squished" putty. Cut your foam (the original are a quite hard rubber, not a foam) to the measured thickness.
Same principle at "plasti-guage"
I'm away from the bike at the moment, but I'll try to measure if method this doesn't appeal to you.