YakyuBaka has a very thorough article, as always, with details and pictures of the uniforms. The Dragons will be wearing their 1974-1986 era home uniforms for two August series' against Yakult. The Swallows will be wearing their 1978 uniform, and it appears that both teams will be wearing home uniforms, kind of weird, but at least both sets are from the same era unlike the other games Yomiuri (1981) vs. Yokohama (1998) and Hanshin (1937) vs. Hiroshima (1975).
Really like the that they are doing this again and hope they continue to do it. I do think though that they should pick a year e.g. 1974 and have every team use that year's uniforms to make things more authentic. I also realize that not all of the teams date back to the 30s, but there are ways around that, as teams could use whatever team was local at that time, it's done frequently in MLB and would add even more variety.
As for the choice of the 1974 Dragons uniform, it's not my favorite of theirs, but I do like it, and definitely prefer the home version over the road.