It's kind of frustrating trying to ID the Martin B-10 or B-12, because there were slight differences just between the B-10A and B-10B...like intake, antenna array and such.
For example, look at the difference between the cowl intake on your sig and the cowl intake on the B-10 at the NASM. The cowl intake raises above and behind the cowl while the intake in your sig shows the intake laying atop the cowl itself.
The intake shown in schnautzer's photo looks to be a bit smaller and angular than the B-10 at the NASM although it is situated behind and above the cowl.