You posted on the Marc McDonald thread that you are writting a high level assembler. I developed cross assemblers and compilers. Put up a bit of information on my web site. It might be of interest to you.
The initial concepts came from work done at SDC in the 60's. CWIC Compiler for Writting and Implementing Compilers. I implemented the syntax and generator language of CWIC with some changes and added the the back end PSEUDO and MACHOP languages to target diferant platforms. CWIC is designed and ran on a IBM 360. With SLIC's MACHOP language machin code is defined in a bit addressable memor space. I don't have all of the PSEUDO and MACHOP documentation online. But you can contact me if needed.