The correct reading of 正和 is Shōwa.
正和 is not the name of an emperor. It is only after Meiji period that Japanese era names are one-to-one corresponding to emperors. The emperor was 花園 Hanazono in 正和 era, and four era names 延慶 Enkei, 応長 Ōchō, 正和 shōwa and 文保 Bunpō were used in his reign.
I'm skeptical about the authenticity of the inscription, by the way. The kanji 和 looks rather strange.