Without additional context, there is no way to tell if there is a difference in meaning.
In these two stories, the sentences mean exactly the same thing:
I met George in 1961 when we worked with Liz and Joanne as caterers. While we were getting ready for a party one night, George told us about his time serving as a soldier in WWII. Before the party, he had been telling everyone how happy he was. But after the party, he described his wartime service as if it had been nothing but torture and humiliation.
I met George in 1961 when we worked with Liz and Joanne as caterers. While we were getting ready for a party one night, George told us about his time serving as a soldier in WWII. Before the party, he had been telling everyone how happy he had been. But after the party, he described his wartime service as if it had been nothing but torture and humiliation.
In these stories (really, the same story), the time of "was" and "had been" is exactly the same: George's time of service in WWII. Once a previous time is established, it's not necessary to keep using the past perfect; switching to the simple past is fine. (See "FumbleFingers' Perfect Truism".) But in this story, which is told entirely in the past tense, there are two past time periods that "was" could refer to: the time of George's WWII service and the time before the party. Saying had been helps clarify that the relevant time is the older time: his WWII service. In this case, the past perfect is optional, not mandatory.
George had a big smile on his face when he arrived at the banquet hall. Before the party, he had been telling everyone how happy he was. But during the party, Susan danced with Mel—and kept dancing with him and dancing with him, and never danced with George nor even spoke to him. By the end of the party, George was no longer smiling.
In this story, it would not make sense to say "…how happy he had been." The time when George was happy was the time just before the party. The past perfect tells the listener that you are referring to a time before the time of the simple past tense. If there aren't two separate past times to contrast, or a hypothetical time to contrast with a real time, then the past perfect has nothing to "point to".
Notice, by the way, that to make the "had been" in "Before the party, he had been telling everyone…" make sense, I had to add something later in the story to explain why I didn't just use the simple past. The past perfect tense tells the listener to look for some sort of contrast between the "had been" time and some other time. That contrast must somehow matter to the story or the listener will likely be confused.
