Terminology

To begin with, let's look at some better names for these two plan types.

Internal Business Plan

A more appropriate name for an "Internal" business plan is a "Strategic Business Plan".

If you think about it, it's real function is to formulate a business success strategy. Thus the term "Strategic Business Plan".

External Business Plan

A more appropriate name for an "External" business plan is a “Funding Proposal” or a “Information Memorandum”.

I think you would agree, that what it's all about. In reality it's usually more a 'selling' or information document, than a roadmap to business success.

Next, let's look at your requirements.