In the prior discussion there is a PDF file showing the location of the embedded reinforcements in the hull that are intended for mounting stern cleats. The OP in that thread gives more information in his narrative about the location.
Your local Boston Whaler dealer may have more information to offer, or perhaps has a similar boat with stern cleats from which you could take a measurement.
You could also contact Boston Whaler customer service to see if they can offer additional information on the exact location of the embedded material.
You can also use available photographs to infer the location. For example, see the image in Figure 1, below:

- Fig. 1. A 170 MONTAUK photograph that shows the location of stern cleats.
- 170MontaukCleatLocation.jpg (127.1 KiB) Viewed 9857 times
Use the photograph to infer the location of the embedded material. In the photograph there are other portions of the boat near the stern cleats whose dimension you can measure from your boat. For example the distance from the transom to the turn in the gunwale downward can be measured from your boat. Next, enlarge that area of the image, as shown in Figure 2, below.

- Fig. 2. A portion of Figure 1 enlarged to permit better measurement of the area of interest.
- closeUpCleatMountingAreaStarboard.jpg (18.36 KiB) Viewed 9855 times
View the enlarged image on a large monitor. Orient a scale so it follows the orientation of the view in the photograph, which may not be perfectly horizontal. On the scale measure the distance from the transom to the turn in the gunwale; note this as variable A. Then use the scale to measure the distance of the cleat base from the transom; note this as variable B.
Find the ratio of the two lengths as variable X:
X = B/A
Measure the actual distance on your boat from the transom to the turn in the gunwale; note this as AA.
Now time for some algebra.
Let BB be the actual distance on your boat to where the cleat base will be.
The actual lengths will be in the same ratio, that is
X = BB/AA
Solve for BB
BB = AA * X
Let's say from the photograph above the value of X is 2. Let's say on your boat the value AA is 5-inches. Then the distance of the cleat base (BB) would be 10-inches.
Find another photographs and repeat the process. If the value of BB remains the same, you have found the dimension you are looking for.
Discovering for yourself the position of the cleat from EXISTING photographs will be more likely to produce useful information than reviving a thread that had been dormant for seven years and asking a participant who has not logged in for four years to go to his boat and take pictures and give measurements to you.