Yea, agree pretty much on the nails, and also that this house has cast butt hinges. That makes it post 1790 most likely. l also agree that 20" is very wide for sub floors for this period, but I just consider this an anomaly as the house is clearly of the post 1790 period.
I'm sure the main house here has a five sided ridge pole. Ridge poles came in to use here about 1790. I believe the Ell here dates the same as the house and there is evidence that clearly shows it was all built at the same time. The photo Jeremy put up of the pass through to the cape second floor to the Ell attic indicates it was always there. The roofers were never cut into and in fact you can see some of the ends of those roofer boards still have the original axe marks at the butt ends. No signs that there was ever any boards closing off that pass. Also the pine floor there is perfectly worn and looks to have always been in use as a passway.
The evidence of there never having been roofing shingle there is a clincher. This Ell was built WITH the house, no question in my mind. (OK, there will always be questions
Jeremy. A VERY good book to pick up would be "Big House, Little House, Back House, Barn"
by Thomas C Hubka. Good section on the Ell and just how it was used and what pride most had in them. Otherwise it's just a great book that all of us old house guys in New England have in our library . It's somewhat a regional book as it's more about the evolution of these building in northern New England.