I recently found some great original architectural drawings of the Nauvoo Temple and Salt Lake Temple. They are on the church's website.
The Nauvoo Temple architectural drawings are found here:
The Salt Lake Temple Drawings are found here:
There are only a few drawings of the Nauvoo Temple, but they do let you see how the design changed over time. The Salt Lake Temple plans are extensive and show numerous changes that are quite fascinating. You can even see what are essentially shop drawings of every course of stones for the temple.
I hope you enjoy these as much as I do.