EOC bare minimum port requirements?

I see from the Orion port requirements doc that EOC requires port 80, 443, 17777

Question: can we get away with opening only port 443? 

Reason: negotiating an EOC feed from an Orion instance in a 'very secured' enclave.  We will never communicate over port 80 (unsecured). 

Usage will be only pull data for reports.  I don't think we will use SWIS functionality (or will we?).

Please advise if I absolutely need port 80 and 17777 for EOC connection or if I can get by with 443.

Thanks in advance for any assistance.