Australian technical publisher Scientific Publications has published a number of Repair/Workshop Manuals which apply to Victa mowers/engines over the past 40 or so years, mostly under their 'Gregory's' banner.
Victa's last self-published workshop manual came out in 1971 [the 'blue cover' one], then Gregory's #102 became the Victa-endorsed 'official' manual, from 1974.
There are two series of manuals in this category; the 'Victa' series, and the 'Small Engines' one - these words appear in the titles.
All of them cover the basic 125cc and 160cc full crank 2-stroke engines,
except for #426.
Four-stroke engine coverage is essentially according to the publication year; e.g. the earlier 'Victa' manuals cover Lauson and Kirby-Lauson 4-strokes. This series does not cover Briggs & Stratton engines at all, but the 'Small Engines' series does cover the vertical shaft models, up to 5hp.
Here's a table I've drawn up, to summarise these manual editions.
Basically, more pages = more comprehensive model coverage. The term 'covers' in the Notes generally denotes the manuals which were the first edition to include info on those carby/engine models.
Availability: All except for #426 are out of print. The best source is eBay AU, and the occasional one pops up in motor bookshops.
Some of them are available to borrow from various libraries; the National Library of Australia Online Catalogue is the best way to track these down.