Hi Simon
I've found I have a photo of him, but it was shared with me by another researcher so perhaps it might be easier to put you in touch directly. Could you maybe send me a private message (PM)?
Remco Hillen also wrote an article about his career which you may have seen already? It was published over ten years ago. I hadn't noticed earlier but you said you had a few of McTavish's records, so I wonder if what I have is partly duplicating what you already have. I note his original certificate of competency was lost in Britannic's sinking but he obtained a duplicate on 10 January 1917. I have his basic career papers and all the crew lists which contain his sign ons for Britannic, which tracks his promotion from when he first joined the ship plus personal details such as age, full name, address etc. After 1917, I've got a record of all the ships he served through to August 1944.
Best wishes
Mark.