Hi, Welcome to JustAnswer.com, I am glad you are here! My name is Eric & I will endeavor to answer your question.
I have discussed this exact situation twice previously with The Chamberlain Group (The Maker of Liftmaster doors openers) Pro Technician support team and both times they have told me (regarding the model numbers I inquired about) That there were none that were interchangeable. I do not believe however, that I insured about your model number or even about a unit that was as old as 1997.
Here is the phone number that you can cal in the morning to make your own direct inquiry. Keep in mind however, that if you are going to buy a new opener anyway, an additional 45 - 60 minutes of your time will replace everything and you will not have a chain and rail system with 15 years of stress on them. I do really recommend just replacing the entire unit along with all of its components
The Chamberlain Group Inc.