Let's start with the one thing that I'm pretty sure about - the regular uniform for the 1973 Nittaku Home Flyers looked like this:
|"The History Of Uniform" page 238|
|"The History Of Uniform" page 239|
|"The History Of Uniform" page 240|
|"The History Of Uniform" page 241|
I'm basing this assumption on the text in the little green circles on the pages. The same text in the circle next to the home uniform on page 238 appears on pages 240 and 241 and the same text in the circle next to the away uniform appears on page 239. This kind of makes some sense as the away uniforms are colored but the home uniforms have a white base. So I think this pretty much refutes the idea that every player on the field was wearing a different uniform based on which position they were playing.
But just to throw some more evidence against that idea, let's look at the two pictures I have of players modeling the uniforms (both of these pictures were taken from a mook - magazine/book - that BBM published last year on uniforms from 1934 to 2013):
The top picture shows (from left to right) Isamu Nakahara (pitcher), Hideaki Watanabe (pitcher), Tsuyoshi Oshita (2b), Makoto Fujiwara (pitcher), Masatoshi Nakahara (SS-3b), Takeaki Yamazaki (pitcher) and Masaki Miura (pitcher).
The bottom picture shows (from left to right) Masayuki Dobashi (mgr), Masaki Miura (pitcher), Naoki Takahashi (pitcher), Shoji Miyazaki (pitcher), Hideaki Watanabe (pitcher), Satoshi Niimi (pitcher) and Isao Harimoto (outfield).
Given that both pictures show Watanabe and Miura wearing the same uniforms, they were probably taken at the same time. Dobashi didn't become manager until mid-season so I suspect the uniforms weren't rolled out until late in the season (but Dobashi was a coach with the team before becoming manager so that's not definite). But what's interesting is that eight of the eleven players in the two pictures are pitchers. That could be just because they were available to model the uniform or it could be further evidence that it didn't matter what position a player was playing.
The only game action photos I've been able to find are on some of the 1973 Calbee cards over at Fighter's Collection web site. All the pictures appear to show the white with orange edging uniform.
So my hope is that someone who can read Japanese can take a look at the text on pages 239-241 from "The History Of Uniform" and tell me what's going on with these uniforms.
One other interesting thing I discovered while I was researching this was that the owner of the Nittaku Home Flyers had proposed a merger with the Lotte Orions. The Orions were having issues finding a permanent home stadium following (I think) the bankruptcy of Tokyo Stadium in 1971. Although I had read that they were playing at Miyagi Stadium in Sendai, apparently they were actually playing games in several ballparks. It's hard to follow the Wikipedia article, but it looks like there might have been another team or teams involved in the potential merger as well. I think the idea was to get NPB down to 10 teams in one league (so everyone could play the Giants), similar to the discussions when Orix and Kintetsu first discussed merging in 2004. I had never heard about this possibility before. Obviously nothing came of it and the Flyers owners sold the team to Nippon Ham who has owned it ever since.