The process I was thinking of is one devised by Tomás O'Canainn in his book 'Traditional Music in Ireland'. This is a system which allows one to analyse a melody in relation to chordal structures. It isn't useful in the situation of comparing ballad airs. What I was doing was confusing O'Canainn's book with another called 'Musical Themes'. The latter is part of a series which allows researchers to compare melodies from Classical works in order to make comparisons. This is a much easier proposition than O'Canainn's analytical method and does allow comparisons. My suggestion would be to take a spreadsheet make fields for title, melodic outline and original Key as a start. Then try the following; (i) Take your melodies and transpose them to the key of C major. (ii) starting with the first note of the first melody use a number to indicate the interval to the next note and the interval from that to the third note etc. This gives a numeric code representing the skeleton of the melody which can then be matched to that of other tunes. The results can be entered into the spreadsheet and then sorted. You should get all tunes of the same type together - just make sure that you have defined a cell which gives the name of the song. I think this process is easily done and should give a quick comparison of any melody type. Remember we are ignoring time signature here. We simply need to know how the melodic shape is formed.
I have used this system in analysing the melodies in the Burnett collection when writing a paper on 'The Hornpipe' and it works well. Where it gets really interesting is when you then use O'Canainn's system to look at how the original tune has been made. You should discover that traditional folk music in England does not follow classical orthodoxy. Many melodies are developed from a single chord whilst others appear to be in a major key but have their dominant, sub-dominant and tonic degrees substituted for one another. I shall not go on. If you want you can read my analysis of hornpipe melodies by downloading the paper from my website.
Hope all this is of some use.
Paul