Jason, nice description, it sounds like a 3 bay side entry English barn. The Snap lines are an interesting touch, snap-line square rule. Are there other similar barns in the area or is this an odd ball? Are there braces in the tie to post position? This is a very common type of barn I see here in coastal down east Maine. Is there a small collar up near the peak nailed in, I am guessing no ridge board and the rafters are butted and nailed? My guess at the date is winter, 1869.

Tim