04-17-2016 07:22 PM
This one is a Wilhelm Hobacher, Wien - ISA as you have stated.
It has the smaller Block hinge hardware but, can also be found with the large based Sheet Metal hinge set up.
Both examples use a "?" style catch directly soldered to the reverse.
Having compared vein patterns with the other so-called Vienna Design family of ISA's...the WH example does match the Orth examples.
One possibility is that one maker was contracted to produce badges for the other...of course, this is conjecture and nothing to verify this argument has been uncovered.
Congrats on adding two nice examples to your collection...
Best Regards, fischer
My greatest fear is that one day I will die and my wife will sell my guns for what I told her I paid for them
"Don't tell me these are investments if you never intend to sell anything" (Quote: Wife)