Hello again Richard
I have looked at the material I already have digitised and unfortunately it wasn't Bourne I had information on but Blount, another of the Dog Boat commanders in the Mediterranean on MTB 634. That said, there is a lot of material on the 60th MTB Flotilla in Dog Boats at War
by Len Reynolds and Flag 4
by Dudley Pope but without knowing which boat your father-in-law served on, I am unsure where to best focus my efforts. You did mention you thought he may have been the flotilla's Leading Telegraphist which if true would likely mean he was with the Senior Officer of the Flotilla on his boat, which would be Basil Laurence Bourne on MGB 645. If this is not confirmed on his service record and/or you do not possess it, then the only possible means of confirming these details would be through obtaining a copy of his service details from the Royal Navy's Disclosure Cell, who you can apply to online.
I do have a further source of information which I will drop you an email about later, but in the meantime I am posting this photo of another boat MGB 646 in the flotilla from the IWM collection available online. Another boat in the flotilla, MGB 647, was that of one of our veterans, Peter, who posts on the forum and there are various contributions from him on the forum including photos.
MGB 647 thread
MGB 663 thread
MGB 661 thread