This is wonderful! This was wonderfully thought out. I know how much of a challenge it can be to line up all of the elements proper and you did a fantastic job!
If I could offer one suggestion though. I think the B&W portion would be stronger if you used the large TIF version found here: http://www.loc.gov/pictures/item/va0248.photos.163747p. The quality of it is much better and it would help to merge into your scene. Also, some of the transition lines from old to new are a little sharp. if you feathered the lines a little it would help to blend better.
I would be happy to help you make a few adjustments if you like, just send me a PM.
A completely new twist on putting a little color in a B&W photo. This is much better, has the spot been marked so that when i next go there I too can take that photo?