oregoncraig - There is no time like the present to begin. Here are a few hard facts and suggestions:
To take the the October 29, 2004 exam you must submit your application (Oregon requirement) by July 15, 2004. This type information, and a lot more required details at these and other websites:
Suggestion - Forget about the October 2004 exam.
To take the April 15, 2005 exam submit you application (Oregon requirement) by January 15, 2005. Only you can decide if this is doable.
Suggestion: Decide wheather you will take Civil (Structural) exam or Stuctural I exam. With a mechanical background, take Civil (Structural), BUT you will have to see (now - not later) if Oregon allows you to practice without a Structural I license.
Suggestion: Look for and enroll in a PE Review course for Structural. This is to accomplish two things: help you determine for yourself if you have a real chance, and if you do - to start preparing for the exam. From looking around the web, you may have to do this online in Oregon.
Suggestion: Take the selected exam at the time you have set (there is no real penalty for failing - and I have seen people come up with excuses & delays lasting a decade or more).
I have taught a continuing education Civil (Structural) PE Review Course for the last two semesters as a local college. What you are talking about is reasonable, over a period of time (maybe a year or two). I do not consider it reasonable within the next 4 to 6 months.
Best Wishes
p.s. I am also an ME who "became" a Structural many years ago.