I heard it first as:

May the roads rise with you,
May the wind be always at your back.
May the Lord smile upon you
And hold you in the palm of His hand.

And sometimes, they added:

And may you be in Heaven half-an-hour
Before the devil knows you're dead.

But I couldn't sing that, and I wanted to. It didn't rhyme and it didn't scan, so I revised it and gave it a simple tune for us simple folk who can't master barbershop harmonies. My wife and I recorded it on our New Harmony LP, also available as a cassette. Goes like this:

May the roads rise with you,
May the winds be gentle where you stand;
May the Lord smile upon you,
And hold you safely in his hand.

May your friends be many;
May they share your joy through all your days.
May the sun shine upon you,
And warm you on your wandering ways.

May your dreams be peaceful in the night.
May you wake to welcome morning's light.

(repeat first verse)

Sandy