Ora,
As you undoubtedly know, I've written the "QB78 Family Workshop Manual" covering the basic steps of stripping and re-building these guns, plus some accessorising. But I stopped at that point - it's 88 pages long already!
To my knowledge, there's no tuning book or article collection available for the QB78 that's in any way comparable to the excellent B50 book. I've certainly thought about producing a QB78 tuning guide, but the amount of time it would take to write - or even compile - such an edition would be daunting. So far, I've not had the time, but it would be a very worthwhile project for someone...
Stephen Archer
Archer Airguns Inc.
http://www.archerairguns.com