Is there a way to find out which ones were bought, torn down, and resold without doing a deep dive into county building permits? 

Under the new laws, unless you are an attorney, real estate agent or lender, you can get in deep trouble contacting people with Notice of Default or Foreclosure status.

For example, I lived on plum street which is relatively deep for college kids (cheaper rent), and we had drug dealers 2 houses down, college kids next door the other direction, and hard working Hispanic group near one corner.

Take a deep breath . . .

I've been nose-deep in turnkey world for about 7 years now.

The US subsidiaries of Canadian banks are leery of financing Canadian purchases in the US unless the borrower has a significant and deep relationship with these institutions in Canada. 

When I was younger and deep in debt with little cash, I was forced to use my day job to build up my cash reserves and pay down my debt.

I have owned 4 of them.. and did well on each.. but very tough to find.. there are some major players on the west coast that dominate it.not nearly the amount of them as I see out in the deep south.. 

Take a deep breath.You have a ton to break down in that long post but let me ask you this.  

Usually when you replace a sewer , you are only opening up about 4 ft wide at the house , and unless its a full basement with a bathroom the ditch is only about 4 ft deep on average .