Nine seventeenth-century organ transcriptions from the operas of Lully / edited with an introduction by Almonte C. Howell. (OCLC #897477805)
The 048 field in MARC is for the Number of Musical Instruments or Voices Code. Each subfield $a typically contains a two-digit code for the type of instrument, followed by a two-digit number indicating the number of parts. This score contains pieces for a single organ player, so the code is:
048 __ ǂa kb01
All keyboard instruments start with k, and Organ is second on that list (ka is the code for piano).