19.69 — Creative Cruciverbalism Solution

Some words have to be put into the grid backward (or upward) in order for the crossings to work (in the grid, they are entries which are entirely in red, though some entries cross so many reversed entries that they have only one black letter). In addition, seven clues are just "..." and these entries are more complicated (shown in bold):

ABACUS PANZA EVEEPTEP
RECIPE INANE SELLIHCA
TAHTISYLTCER INNEREAR
SKYE SSUESRD ADIV YRW
MYST ONER NEEB
TACTILE WALAL NONABEL
TEHTNUMBER GRE ROTE
ARAIT ALF ERIC ATLAS
MADA JACK BLEAK RHONE
REAP REACH TNAFNI
PRO RGEDRAHCOCKNI GID
REGNAS REFAS RA
EN
EVAEH CAPON EKIP ENAZ
FINKS AMOS ECI HSABA
ALDA SAM NIDLIUBTEN
BODEREK ARMOR AMNESTY
NWOT SNAS ENAK
EKI CAME CIRENEG WOLB
DAFFODIL IDABOVEEHTLA
ETODCENA NAMUH REIPOC
NEUROSIS ESORP YZTULK

The ... answers need to be rearranged into an order so that the partial words at the end of each answer form proper words. The full string of words alternates between forward and reversed words. The reversed words and word parts are shown in parentheses here:

64D: (GO) AND (FIND) OU
44A: T (THE) NUMBER
23A: (THAT) IS (RECTLY)
115A: (DI) ABOVE (THE) LA
65A: RGE (HARD) COCK (IN)
17D: THE (LOBBY) OF (G)
89A: (BUILDIN) TEN 

Fully assembled, it reads: GO AND FIND OUT THE NUMBER THAT IS DIRECTLY ABOVE THE LARGE HARD COCK IN THE LOBBY OF BUILDING TEN.

Building 10 is dedicated to RICHARD COCKBURN MACLAURIN, a president of MIT from the early 20th century, and his name is carved in stone in large letters in lobby 10. Directly above the HARD COCK in his first and middle names is the number SIXTEEN, which is the answer.

This inscription (but not the 16 above it) can be seen in this photo from the Hall of Hacks.