Yes, I think Italeri now owns, or has obtained the Supermodel moulds.
As far as I'm aware this is the only injection moulded Z506 on the market. Cross kitting it with another manufacturer to correct dimensional errors is no help.
Personally, the model looks in proportion to me when built up, so to coin a frase, "if it walks like a duck, quacks like a duck then it's a duck", or a Cant Z506, which ever you prefer.
To be completely honest a few mil discrepancy here & there does'nt bother me, I'd much rather enjoy the build & have the finished model on the shelf than worry about a few mil.
