Well, George, I think you may be right after all. I did some more digging and I'm convinced that this score was set on Difficulty 2 (MAME Medium), and NOT the TG Arcade setting of Difficulty 3 (MAME Hard).
Your initial look at the coconuts didn't convince me, as I explained, so I started looking for some other things to measure. The Bonus Timer would have worked, but it's not visible in your video. So, I ended up using the rate at which Kong descends on the vines (ropes?).
Below is a table that gives the rate, in frames, at which Kong descends for every "step" along the way. As you get deeper into the game, the rate increases. For example, on Difficulty 1, on Board 1 Kong takes 65 frames for each drop. On Board 6 this speeds up to 57 frames per drop. All Difficulty levels reach the maximum drop rate by Board 27. There are things that cause Kong to pause (spraying him, coconut throwing) but he always resumes his descent at the drop rate for that board. The counter that determines when he moves will actually pause during those spray/coconut moments and then pick back up in same spot when those animations are finished. Anyway...
I downloaded Part 1 of your video and used VirtualDub to examine it frame-by-frame. There are 4 boards that I think conclusively prove this was on Difficulty 2 settings: Board 3, Board 12, Board 18, and Board 21.
On Board 3, your video matches the 57 frames per drop rate. Looking at the table below, that value matches both Difficulty 2 and Difficulty 3. So, that rules out Difficulty 1 and Difficulty 4. On Board 12, your video matches the 51 frames per drop rate, which would match both Difficulty 1 and Difficulty 2. However, Board 3 rules out Difficulty 1, so we're left with Difficulty 2.
To make sure the video quality wasn't interfering with my analysis, I checked Board 18 and Board 21 as well. Both boards match the value expected for Difficulty 2. Board 18 was too slow to be Difficulty 3 (but matches Difficulty 1). Board 21 was too slow to be Difficulty 3 but too fast to be Difficulty 1.
Let me know what you think. At this point I will probably move this score over to the Difficulty 2 Marathon HSL, replacing your 6.1M MAME score. I'll also need some links/INPs for your best actual Difficulty 3 score. And speaking of INPs, you should post the ones you have for your 1.5M Difficulty 2 5-man, 2.4M Difficulty 4 Marathon, and 600k Difficulty 4 5-man.
Frames Between Each Drop (at 60 frames per second)Board | Difficulty 1 | Difficulty 2 | Difficulty 3 | Difficulty 4 |
Board 1 | 65 | 65 | 57 | 57 |
Board 2 | | | | | | | | |
Board 3 | | | 57 | | | 51 |
Board 4 | | | | | | | | |
Board 5 | | | | | | | | |
Board 6 | 57 | | | 51 | 43 |
Board 7 | | | | | | | | |
Board 8 | | | | | | | | |
Board 9 | | | 51 | 43 | 33 |
Board 10 | | | | | | | | |
Board 11 | | | | | | | | |
Board 12 | 51 | | | | | 26 |
Board 13 | | | | | | | | |
Board 14 | | | | | | | | |
Board 15 | | | 43 | | | 20 |
Board 16 | | | | | | | | |
Board 17 | | | | | | | | |
Board 18 | 43 | | | 26 | 13 |
Board 19 | | | | | | | | |
Board 20 | | | | | | | | |
Board 21 | | | 26 | 20 | | |
Board 22 | | | | | | | | |
Board 23 | | | | | | | | |
Board 24 | 26 | | | | | | |
Board 25 | | | | | | | | |
Board 26 | | | | | | | | |
Board 27 | | | 20 | 13 | 8 |