On Youtube there is an overdub version of Danny Boy that I have not heard before. It is titled

'Jim Reeves "Danny Boy"'

Youtuber is JamesTJordan1
I think it is an RCA overdub from the 60's or 70's and possible RCA 45EP/20401 which is shown on the video.
As I say, its new to me me.
Thanks all.

While searching for this I also found Jim Reeves Danny Boy HD with lyrics.

I think both are slightly different from the one we are familiar with.

The photos with the HD version are quite nice.

Just played it and I think you are right. Very slight difference. Don't think I would have noticed before.

Have come across some details now. The original recording was 30th January 1961. The overdub was 28th February 1975 by Jerry Bradley, Strings by D.Bergin White. I had it all along, just didn't know. (The Unreleased Hit's CD).