Interestingly, you can print a non for safe object when for safe filaments due to the surface finish likely being too porous to clean properly.
I think I'll stick to some cookie cutters.
The Prusa Mk2S extruder instructions have 35 steps whereas the Mk3 extruder instructions have 66 steps, mostly as the later has more small odd metal parts.
I was thinking about trying to construct a Mk3 extruder assembly, but I'm put off for the moment by trying to source the odd parts.
If I had planned differently and had not bought a 5th stepper motor and a hotend already then
I could order this kit from aliexpress which appears solves the sourcing problem
tidily.