Here are some of my test results for orientations of Morse Code to see if Palimpsest can be recovered.

#1  Straight 81, left to right across the rocks

DIGETALINTERPRETATIUTISYOURPOSITIONVIRTUALLYINVISIBLESHADOWFORCESLUCIDMEMORYSOSRQ

Distance between P’s: 14 (or 67). 14-4 = 10. 10/5 = 2. Distance to nearest M =42 (or 39).

PreTatIutIsyOurP PTIISOP, the method does not recover palimpsest.

#2  Straight 81 Backwards, right to left across the rocks applying the palindrome concept that we read it from the other side to get a different message

QRSOSYROMEMDICULSECROFWODAHSELBISIVNIYLLAUTRIVNOITISOPRUOYSITUITATERPRETNILATEGID

Same as above, distance between P’s: 14 (or 67). 14-4 = 10. 10/5 = 2. Distance to nearest M =42 (or 39).

Due to the use of equal key lengths, the letters POSIITP are recovered (the reverse of the above).

It would be odd to consider a key-length of 2 because we should be able to “see” plaintext mixed with plaintext if we’re observant enough. All the same, it was not a number I picked but a product of the Morse Code string chosen.

#3  Straight 106 (with E’s), left to right across the rocks

DIGETALEEEINTERPRETATIUTISYOURPOSITIONEEVIRTUALLYEEEEEEEINVISIBLEEESHADOWEEFORCESEEEEELUCIDEEEMEMORYESOSRQ

Same as #1.

#4  Straight 106 (with E’s) backwards, right to left across the rocks applying the palindrome idea

QRSOSEYROMEMEEEDICULEEEEESECROFEEWODAHSEEELBISIVNIEEEEEEEYLLAUTRIVEENOITISOPRUOYSITUITATERPRETNIEEELATEGID

Same as #2.

These are perhaps a better verdict that the key-length is not 2, with all of those strings of E’s the message would be garbled.

#5  Two Rows from left to right

DIGETALTISYOURVIRTUALLYSHADOWLUCIDRQ
INTERPRETATIUPOSITIONINVISIBLEFORCESMEMORYSOS

Distance between P’s = 7,  7-4=3, 3/5 is not a whole number

I kind of like this one anyways so I’ll try and force it a little.  If we try every fourth letter we get P-A-P-T-I-S-E-C-E-Y-D-T-I-U… we’ve skipped both M’s and have a C and no B (for abscissa).
Every 7th: PPIEE skips the M’s as well

#6 Two Rows from left to right with the E’s

DIGETALEEETISYOUREEVIRTUALLYEEESHADOWEELUCIDEEERQ
INTERPRETATIUPOSITIONEEEEEEINVISIBLEFORCESEEEEEMEMORYESOS

Unfortunately, not much has changed between those two P’s.  Perhaps we can retrieve an M?

Every fourth: PAPTEEVBOSEMEDTESRIAEHWUEQE
Can we get palimpsest out of that?  No, there are no L’s.

Every 7th: PPEVOEE  We end up skipping the M’s.

-Kryptos Fan