You might reasonably question his conclusions but I don't think you can mount much of an attack on his scholarship. At least no one has to this point. Not Heise nor Robinson.
UnderGround 1
UnderGround
from Urban Underworlds, chap. 4, Thomas Heise, Rutgers University Press, 2011
I might also call your attention to page 315 of this thread, there is a bit of a discussion on this subject between E_R and RickM. Interesting stuff. By the way, my copy of Tarnished Angels which I found a couple of months ago weighed in at $75. ouch.