This set of photos of 186 was taken before 186 was stretched, probably by a Lockheed photographer. They were sent in to C141Heaven by Dave Grant. The exact date and location is unknown.
This was the first C-141 to be 'stretched'.
YC-141B after the 'stretch' plugs were installed, but not yet painted
Source: Steve Quigley
First flight of the YC-141B after the 'stretch'.
66-0186 on the ramp after the stretch.
65-0269 parked next to it in 'stubby' mode.
Source: Lockheed photo from the collection of Paul Minert
Here's five pages from the February 1979 MAC Flyer regarding the stretch program
Source: Paul Minert
Copyright ©: 1978 Michael Grove. Note the tail flash.