My opinion is that the development conditions are too weak for this emulsion. It should give a good contrast image with a reasonable exposure using about ISO 3 which is probably faster than what you saw.
I have one of his plates right here on the table next to me. Here is a scan of it courtesy of Mark. As you can see, it has good density and contrast.
I have posted a series of Mark, pouring this emulsion, in another thread here.
I think you have used too little developer A and B.