As for mic techniques, all the instruments in Nelson’s records were individually miked.
One U 47 over the drum kit picked up the entire set (based on other musicians’ session photos of that era).
For example, Figure 4, below, shows the drum miking at an Elvis Presley session.
SESSIONS
Master Recorders had isolation booths shaped like little cabins with windows. As the band played in the studio, Rick sang in a booth while listening over headphones.
Sessions were recorded on either 1, 2, or 3-track recorders, usually with several generations.
All the Imperial recordings followed this sequence:
1. Instrument tracks were recorded with Rick doing a guide vocal as a reference. Most of the instrument mics were mixed live to mono or stereo.
2. Rick overdubbed the lead vocal.
3. Rick overdubbed acoustic rhythm guitar and occasionally some other vocal parts. At least two guitars were used on all the recordings.

Figure 4: Mic techniques at one of Elvis’ sessions. Source: scottymoore.net. (click to enlarge)
4. The Jordanaires overdubbed their backround vocals later when they were in town. Sometimes they would add their harmonies to an unfinished track that had no lead vocal. They worked out the arrangements with Rick in the control room.
After a few years, singers Burgess, Fuller and Campbell replaced the Jordanaires, who were busy with Nashville sessions (Figure 5).
After BF&C added their vocals, Rick would come in the next day to say what he liked and didn’t like, and the singers re-did their parts as needed.

Figure 5: Rick and the band. (click to enlarge)
Engineer Robyn sometimes would take the first part of one take and the second part of another take, and splice them together.
A typical session of two complete recordings lasted 3 hours.
EFFECTS AND EQ
As for effects, it’s easy to hear the tape slapback echo in the 45 single version of Be Bop Baby. The album version of the same song was mixed with plate reverb instead, and in my opinion the slap echo was much more effective for that song. Most of Rick’s songs used a lot of plate reverb.
James Burton got his unique twangy tone by using fingerpicks and a flat pick on his 1953 Telecaster guitar. He replaced the first four strings with banjo strings, then replaced the A string with a D, and replaced the low E string with an A.
As James says, “I already had my sound. The tone of my guitar is the sound we went for and what I like and what we basicially did on all the records”.
In Rick’s early recordings, they used an acoustic bass rather than an electric. The result is a pulsing, buoyant bass sound that an electric bass can’t provide.