I think the problem here is that you are very experienced with PL/M, but a novice with 'C'. Yes?

The transition from one language to another is never trivial, but to go to a language you've never used before...

I think you probably need to take some time-out to learn 'C' before you dive straight in and attempt to do what is now second nature to you in PL/M.
(and when you do it, make sure you learn 'C' with a small-system embedded emphasis; if you go on a UNIX systems course, that'll just scare you off even more!)