I finally got the porch taken down and have started getting the house ready for attempt number two. I promised to explain what happened.
See, there was this really bright light and then suddenly I found myself in a craft looking at two grey aliens holding what looked like a probe of some kind. Oh wait. Wrong story. Please disregard. I need to up my medication.
Ok then. When I removed the soffits this is what I found.
Was that It? No, not by a long shot. When I started taking down the aluminum ceiling I found the joists for the other section of the roof. Yes, they were complete and there were no add ons but a closer look revealed this.
This is another look at this section of the house. You can see the roof and where I put up the header/nailer for the joists at the back. That's the section I'm talking about. There is some good news. See those two posts left and right in the picture at the back of the structure I built? Those are supporting a doubled 2x6 header for the existing wall. I took the roof back to that header and I'll now use it as the nailer for the new joists. After I get the new joists up I'll be able to see how much of the soffit I'll have to remove for the roof to fit. I'll be judicious and may find a way to reinforce the old roof joists but I'm confident it'll be plenty strong enough.
The structure is now down and I'm measuring and planning the new build. I'm confident I have now identified all the problem areas and fixes that will work, be structurally sound and look good. I'm also going to follow KurtP's suggestion and make both of the unsupported perimeter joists true 4x6 headers and add in at least one more 4x4 post for support. I'm ever rethinking 24 inch on center joists and may go with 16 inch. Time and budget will tell.
What have I learned from this fiasco? Do your due diligence. If you're going to add something make absolutely certain you do a proper tear out and discover all the hidden issues before you drive a single nail or cut your first board. Trust me, it's a lot less painful that way.