[link to original on tumblr]
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I'm pretty sure I noticed this the first time I listened to the album, but I haven't written about it: in that version of "Hold Your Head Up," Rod Argent includes half of a hymn tune in the solo (he plays it twice from about 6:01 to 6:26). I know it best as the tune for "God of Grace and God of Glory," but the tune itself is known as "CWM Rhondda" and was written by John Hughes.
Argent includes some variations, but the original part that he quotes is: