The MR is also the PrePro3, not the ESB. They're almost identical... Almost. The guy MR hired to paint the prototype from the helmet Lucasfilm sent them pointed this out, but the Lucasfilm Archives people refused to accept they'd made a mistake and swap helmets. So MR shrugged and went ahead with the helmet they'd been sent.
Also, are people forgetting the nice, hard-plastic, 1:1, $50 Boba helmet Rubies put out a couple years ago? Yeah, there are a couple concessions to injection-molding that need to be addressed, and it needs to be repainted, but there are good, accurate stencils out there. Since there was discussion of not having a good base to work from, and there is, I thought I'd point that out. A PCR will probably retain the horrid asymmetry of the original. So there's that. Me, I prefer the symmetry of the Rubies lid.