I purchased the right outboard (#4 engine) nacelle from the New England Air Museum on October 12, 2018.   Kim Jones, a long time docent and volunteer, was instrumental in helping me to acquire this and parts for my B-29 QEC (engine, mount, and cowling) display.  The nacelle is from B-29A 44-61975.  This B-29 had been recovered from Aberdeen Proving Ground, Maryland in 1973 for their museum, which at that time was named the Bradley Air Museum.   When disassembling the aircraft at Aberdeen, the aft fuselage was so badly damaged that the Army allowed them to take the aft fuselage of 44-61739 instead.  They had not completely reassembled the aircraft when the devastating tornado on October 3, 1979 hit the museum.  At least 20 aircraft were completely destroyed and the B-29 was hit by at least two other aircraft.  The #4 engine (right outboard) was ripped off of its nacelle.  They removed this damaged nacelle from the aircraft and replaced it with one from 44-61739.  My nacelle is the damaged one from 975.  It had sat outside nearly its  entire life since WWII, so it has considerable corrosion, plus  bent, damaged, and missing metal from the tornado and from parts utilization in the replacement nacelle.  

The nacelle was constructed by Fisher Body Corporation, a division of General Motors, in their Cleveland, Ohio Aircraft Plant No. 1.  They built at least 80% of the engine nacelles on B-29s.   Many of the parts on the nacelle have "FBC" inspection stamps.   A number of panels and hatches are labeled as either "975" or "739".

After studying  numerous WWII and more modern publications and photos, I was able to determine some of the parts which were missing on the nacelle.  I realized some of those were at the New England Air Museum, but I didn't realize at the time they went to it.  I made a second trip there beginning November 2, 2018 and shipped back a whole crate of parts, mostly for the nacelle.  Once again, Kim Jones was extremely helpful in this effort.  Deborah Reed, Executive Director of the museum, approved the reasonable prices I paid for the nacelle and parts for my B-29 displays.  If you get a chance, go see their incredible museum and see the now beautiful B-29 painted as "Jack's Hack".