Thanks! The plans are 30"x15". I was saving them as "highest quality" (I don't know what actual resolution that turned out to be), which was probably overkill. I reduced the resolution when initially importing the PDF in Photoshop from 200 ppi to 100. (The default 72 ppi still left things a little grainy) and saved as a PNG. One or the other (or both) took care of the problem. The resulting PNG file is only 500K and inserts into LayOut just fine.

It's a .PFM font, which I think came originally through Adobe. It appears on my list of available Text Styles in Layout - but that list must just be generated from whatever fonts I have in C:\Windows\Fonts?