Soft Echo of Timing Issues

While the question itself serves to point out that I should tape out a proper outline of the movement . . . my friend Brian, on reading this, inquired where those seven measures of 3/4 are situated. The question is a nice challenge to describing where, when the inquirer lacks a score.

There are two ‘singletons’, peppered in for occasional effect (as it were):

• m. 30 near the start of the opening ‘big A’ section
• m. 147 in the ‘big B’ section, which begins with the strings running a unison [ g-a-b-flat-a (repeat) ] sixteenth-note ostinato
  

In between these, five of the 3/4 interspersals (mm. 68, 71, 77, 87 & 90) are a regular part of (as one readily hears, I think) the brass chorale (the answering theme in the ‘big A’) which begins with the repeated eighth-note pickup to (the first such measure) 67. In octaves the first trumpet and trombone play [ B-flat.B-flat / E-flat - D-flat / C C ] . . . the E-flat is a half-note, and the D-flat, a quarter-note, in a bar of 3/4.