Hi fromwien, you don't have to apologize, it was exciting to find the solution to your puzzle!
Indeed, this deserves further study. For example, to me it is only a modified TZ2 frame, and it was used to build the Tiger (and here I take this opportunity to thank Trefoil, thanks to his question about the Tiger he gave me the answer to another puzzle) and then the name of the Shepherd , an old OP mechanic said it was an OP Cobra ....