Tom,
Usually it's rare when that type of thing is digitized and online, and I think you're heading in the right direction by going to the Montgomery County governmental archives. If professionals were out there measuring and sub-dividing and creating contour maps, and such, I'm betting there might be a great find hidden in those vaults.
At this stage, I'm almost hoping for it to be as simple as what David and Sully believe in terms of swapping for that triangle before November 1910, but I just can't fit the other pieces into that puzzle, try as I might. That accounts for my repeated questions to them, which with all due respect, I don't think have been convincingly answered.
I say that I wish it were that simple as all that, because I also completely agree with Jim Sullivan that nothing meaningful about Hugh Wilson's role or lack thereof in the creation of Merion East flows from any finding about when that Francis Swap event happened.
Conceptually, I agree with Jim that guys who were the best club golfers and local "experts" like Wilson and Griscom et.al. would have been out there envisioning holes before the property was originally purchased, because that's what we would be doing if we belonged to a club and had the opportunity. Heck, that's what you did at Ardrossan, and that's what some of us are doing at Cobb's, so that part makes sense to me.
However, there is simply no record of any of that really happening between July 1910 and November 1910, a really good record of what happened from November thru April 1911 and beyond (that seems to include most of the routing and design activity).
David's essay wanted to use that gap, as well as the presence of a letter from CBM (before it was actually found and its contents disseminated) as evidence that CBM must have routed the course, but we now know that's not true and that after his initial one-day visit in June of 1910 didn't return to Merion until the project was almost ready to go, on April 6th, 1911.
So, at the end of the day, I think it really matters not a whit whether Francis had his bicycle ride before Nov 1910 or after. I can understand Jim's argument for it to happen before, but can't make the other pieces fit, as mentioned.
However, whether it actually matters or not regarding actual architectural attribution of Merion, you can bet if you find that map I'll be the first one over your house.