What I suggest is using the Text Encoding Initiative (TEI) Guidelines which is the de-facto standard for encoding text in the humanities (which the VMS is). It is very flexible and ensures future data sharing with others, as well as support from future text-analysis software.
The V4 Guidelines sprawl out from here: http://www.tei-c.org/Guidelines2/index.html
If my suggestion is accepted, I may prepare a suggested subset of TEI tags for encoding the VMS interlinear file.