[racingdwarf]

I think they are kit, I was changing some on my sons car and noticed the same thing on the std kit ones on the car, no marking, seems a bit of a strange thing to do as you would think all the caster blocks come from the same production line. maybe the spares are made at a different place to the kits

The other interesting thing is on the exploded view in the parts manual the caster blocks have no part number shown but the parts list shows TLR1057 10 degree all other blocks are in the options section, so I guess your deduction is correct