Some useful feedback from Lou on the TEI list about where to encode the info relating to the journal issue and volume. As a result, I've now moved the journal title itself into <seriesStmt>, along with the other related info:

           <seriesStmt>
                <title level="j">IALLT Journal</title>
                <idno type="vol">39</idno>
                <idno type="issue">1</idno>
                <respStmt>
                    <resp>editor</resp>
                    <name>
                        <forename>Heather</forename>
                        <surname>McCullough</surname>
                    </name>
                    <name>
                        <forename>Douglas W.</forename>
                        <surname>Canfield</surname>
                    </name>
                </respStmt>
            </seriesStmt>

I have a couple of issues still in discussion on the list, including how to encode the text type; I think the best solution would be this:

   <profileDesc>
      <textDesc n="article"></textDesc>
   </profileDesc>

where the @n attribute is constrained to a list of fixed values by a modification in the ODD file. Still waiting for feedback from the list on this.

Finally, I wrote to the IALLT folks to check whether it would be OK to use a block of their metadata in the TEI Guidelines, once all this is agreed on.