Misplaced Modifier in a Common Hymn?

Okay, this is pretty random, but for my Advocacy class, we have to keep track of our grammar.

So a minute ago, while I'm reading Justice Scalia's dissent in Locke v. Davey, 540 U.S. 712 (2004), I come across a phrase with the word only in it.

I've struggled with this modifier for a long time and it made me think of a hymn that actually misuses it:

There Is a Green Hill Far Away

There was no other good enough To pay the price of sin. He only could unlock the gate Of heav'n, and let us in.

http://www.hymnwiki.org/There_Is_a_Green_Hill_Far_Away  (4th stanza/verse)

Ever since I was a kid, this phraseology confused me, and now I understand why!

Only is supposed to modify the word or phrase immediately following it.

http://writing911.com/writing/good-writing-tips/grammar/watch-where-you-place-only-in-your-sentences.html


So in this case, it should be "Only He could unlock the gate . . ."  Otherwise, it means that all He can do is unlock the gate and let us in, but from the preceding text, it's clear that the purpose of the stanza is to say that He is the only one who can take the action spoken of.

Maybe I'm reading too much into the only bit, but it seems to me like the intention is to say only He could do all this (and not all He could do [expressing limitation] is this).

By the way, I'm pretty sure this stanza is an LDS revision of the hymn, but it seems like the original or more common version has the same issue:

http://www.lyricsondemand.com/miscellaneouslyrics/christianlyrics/thereisagreenhillfarawaylyrics.html