Good news; I got my wish - my first 2-way average of 60 MPG + during my first mileage test run with the "new" engine!!
It's "preliminary" because I haven't calibrated the ScanGuage since the engine transplant, so don't know if it'll change.
The "mediocre news" is I had to drop down to 35 MPH before it registered 60 (62.4 north & 63.0 south - avg = 62.7). At 40 MPH it was just short; 2-way avg of 59.45. But it was over 50 MPG at all speeds below 50. I didn't test it at 55, but since it got 46.25 at 60, I suspect 55 would have been 50+ MPG, too.
These were all on my 4.5 mile test course.