A PD Multi Baby! Gateway To Heaven?

On 05/07/2023, I found GC8AJAC - Pointerdoggs 1000th- 'Cache within a cache' cache.

I placed three Pre-form Containers into the container and removed two Peanut Butter Jars with the intention of hiding them somewhere in due course. 

This is the first of those two Peanut Butter Jars which was removed during that visit that I have hidden and I believe this listing is also the first multi-cache to be born as a result of the PD Cache Breeding Programme™.

This is a straightforward multi-cache.  Go to the posted co-ordinates, make the required observations, note the required information and calculate the final co-ordinates using the formula further below.

There are numerous ways to approach the posted co-ordinates but the easiest way is to park at the free car park on the B27 Moyard Road at N 54° 07.542 W 006° 02.160 (waypoint added).  From there, follow the well defined track along Banns Road, heading NNE until you reach the posted co-ordinates. 

Here, you will meet the Mourne Wall, a stile and a metal gate.  Beyond the metal gate, is the gateway to ‘Heaven’, or in this case, the Mourne Mountains.  At the metal gate, there are two large metal supporting posts, one on either side.  It doesn’t matter which large metal supporting post you look at, they are both the same.  Observe and note the THREE LETTERS at the top of the large metal supporting post. 

To calculate the values of ABC below, assign a numerical value to these letters, according to their position as they appear in the alphabet.  A is the first letter that appears, B is the second letter and C is the third letter.

For example, if the three letters at the top of the large metal supporting post were FGH, the values for ABC would be as per below:-

The cache can be found at:-

The total checksum for all numbers in the final co-ordinates is 46.

In addition, a spoiler photo is available in Certitude.

You can validate your puzzle solution with certitude.