Look at Bill "Revisions". 

My understanding was that bill revisions were to track bill of material changes and to be used with "Engineering Change Order" numbers so BOM's would be updated on the effective date of the ECO. Are revisions to be used as alternate BOM's?

It's just an idea that may work.  Sage 100 is a feature-rich program and how you choose to use the features depends on your business needs. 

Working with your Sage Partner is probably a good idea when devising a strategy for a complicated implementation.  In addition to the core Sage 100 program there is a significant eco-system of enhancements / add-ons which might make your life easier, and Sage Partners can help you find the right solutions.