Not sure if I have the right method but here is how I got it:

Make pairs

3n 2x 2a 2f 2e 3c 3d 2s 3f 2o 3h 2w 3j 2s 2e 2d 2g 3d 2p

 The keyword section logically his 3c 3d 2s 3f 2o 3h 2w 3j 2s. Using the Regex string ^..(.).....\1$ reveal that the only possible keyword is operative.

The decimal values to get OPERATIVE are 79 80 69 82 65 84 73 86 69. The formula to get these numbers is (n*26)+(l-1) where n is number and l is letter using a=0

Do the math for each pairs

90 74 53 56 55 79 80 69 82 65 84 73 86 69 55 54 57 80 66

Convert decimal to Ascii

ZJ587OPERATIVE769PB

There is probably a mistake in the code, the 2a should be 3a which would give 77 which convert M

ZJM87OPERATIVE769PB

Make pairs

68 61 66 33 35 66 00 07 41 32 36 36 6b 67

Convert hex to Ascii

haf35fA266kg

The prefix and suffix work great but we need a keyword substitution

Searching 66000741 on Wikipedia gives the NRHP Reference to Danger Cave

haf35danger266kg