Question: What size aperture did the telescope which was used to discover NGC 331 have?

Context paragraphs:
Multicolor Active Galactic Nuclei Monitoring: Multicolor Active Galactic Nuclei Monitoring or MAGNUM was a project completed in 2008, that used a 2 meter (78.7 inch) telescope at Haleakala, Hawaii.  The project started in 1995, and with telescope observations starting in 2000 for the scientific study of active galactic nuclei.  It was run by the University of Tokyo, the National Astronomical Observatory of Japan, and Australian National University.  MAGNUM was one of the telescopes that observed a cosmic explosion billions of years away in 2005.  The telescope was used for a long-term study of the size of the universe; for example it studied the Seyfert 1 galaxies NGC 5548, NGC 4051, NGC 3227, and NGC 7469 The telescope was located at the Haleakala Observatory and was installed in north dome previously used by LURE.

NGC 384: NGC 384 is an elliptical galaxy located in the constellation Pisces.  It was discovered on November 4, 1850 by Bindon Stoney.  It was described by Dreyer as "pretty faint, pretty small, southwestern of 2." , the other being NGC 385.  Along with galaxies NGC 375, NGC 379, NGC 382, NGC 383, NGC 385, NGC 386, NGC 387 and NGC 388, NGC 384 forms a galaxy cluster called Arp 331.

NGC 385: NGC 385 is a lenticular galaxy located in the constellation Pisces.  It was discovered on November 4, 1850 by Bindon Stoney.  It was described by Dreyer as "pretty faint, pretty small, round, northeastern of 2." , the other being NGC 384.  Along with galaxies NGC 375, NGC 379, NGC 382, NGC 383, NGC 384, NGC 386, NGC 387 and NGC 388, NGC 385 forms a galaxy cluster called Arp 331.

NGC 388: NGC 388 is an elliptical galaxy located in the constellation Pisces.  It was discovered on November 4, 1850 by Bindon Stoney.  It was described by Dreyer as "very faint, small, round."  Along with galaxies NGC 375, NGC 379, NGC 382, NGC 383, NGC 384, NGC 385, NGC 386 and NGC 387, NGC 388 forms a galaxy cluster called Arp 331.

Francis Preserved Leavenworth: Francis Preserved Leavenworth (born September 3, 1858 in Mount Vernon, Indiana; died November 12, 1928; a.k.a. "Frank Leavenworth") was an American astronomer.  He discovered many New General Catalogue objects together with Frank Muller and Ormond Stone.  They used a telescope with a 66-cm aperture at the Leander McCormick Observatory at the University of Virginia in Charlottesville, Virginia.

NGC 375: NGC 375 is an elliptical galaxy located in the constellation Pisces.  It was discovered on September 12, 1784 by William Herschel.  It was described by Dreyer as "pretty faint, small, round, brighter middle."  Along with galaxies NGC 379, NGC 380, NGC 382, NGC 383, NGC 384, NGC 385, NGC 386, NGC 387 and NGC 388, NGC 375 forms a galaxy cluster called Arp 331.

NGC 380: NGC 380 is an elliptical galaxy located in the constellation Pisces.  It was discovered on September 12, 1784 by William Herschel.  It was described by Dreyer as "pretty faint, small, round, suddenly brighter middle."  Along with galaxies NGC 375, NGC 379, NGC 382, NGC 383, NGC 384, NGC 385, NGC 386, NGC 387 and NGC 388, NGC 380 forms a galaxy cluster called Arp 331.

NGC 331: NGC 331 is a spiral galaxy in the constellation Cetus.  It was discovered in 1886 by Francis Leavenworth.  It was described by Dreyer as "extremely faint, very small, round, a little brighter middle, 12th magnitude star 3 arcmin northeast."  There are two candidates as to which object is NGC 331: PGC 2759 or PGC 3406, with the former being a much more likely candidate than the latter.

NGC 387: NGC 387 is an elliptical galaxy located in the constellation Pisces.  It was discovered on December 10, 1873 by Lawrence Parsons.  It was described by Dreyer as "very faint, small, round."  Along with galaxies NGC 375, NGC 379, NGC 382, NGC 383, NGC 384, NGC 385, NGC 386 and NGC 388, NGC 387 forms a galaxy cluster called Arp 331.

NGC 386: NGC 386 is an elliptical galaxy located in the constellation Pisces.  It was discovered on November 4, 1850 by Bindon Stoney.  It was described by Dreyer as "considerably faint, small, round."  Along with galaxies NGC 375, NGC 379, NGC 382, NGC 383, NGC 384, NGC 385, NGC 387 and NGC 388, NGC 386 forms a galaxy cluster called Arp 331.

Supporting paragraphs: NGC 331 Francis Preserved Leavenworth
Answer: 66-cm