They modeled after a later style VEGA lens, not the earlier Lucas. The important part is that they don't fit where the Lucas lens did. I assume that the lens must shrink when it comes out of the mold. Its smaller in almost all dimensions. The critical part is the spacing of the mounting holes, which is a whole hole width off.
If you egg the hole out a half a width on either side, they'll sorta fit.
I complained that they were sub-standard, but didn't ask for anything else.... and the seller gave my money back. So at least he's honest.
Just thought any Imp or Humber owners should be aware of what's out there.
We still have the original lenses in stock. Both new and used.
Some units are avaliable too.