The Macmath Collection at Kirkudbright would make a great project for publication. The only person I know who has researched in there is Ronnie Clark who published the Elizabeth Sinclair Ms. I suspect it would take several researchers. I don't know of anyone in that area with the time, the resources and the motivation. I suspect he sent any material that was relevant to Child but it would be useful to read his correspondence to know his opinions on various aspects.