Hi.
If by
cobalt, you mean COBOL, the business-oriented language, then you may be interested in:
OpenCOBOL - an open-source COBOL compiler
I have used that compiler (really a translator, it "compiles" to c, but that's a minor detail) for demonstration tasks. The version I used was in the Debian GNU/Linux repository so it was very easy for me.
The COBOL programmers with whom I had contact were fairly isolated from the raw machine (although I knew a few who did binary patches ! ), so unless there are real hardware dependencies, I don't think you would need a custom kernel.
So, I agree with fpmurphy -- try porting the COBOL user programs first to a new computer with a new OS (but one that is easy to install and use -- ubuntu comes to mind), and something like OpenCOBOL, then if that fails, you might try a custom kernel, but I consider the latter more difficult.
Best wishes ... cheers, drl