Welcome to the forum, Jarrod
Gregory's Number 424 Victa Rotary Mowers Service and Repair manual ISBN 0-85566-690-0. Covers early 125cc, early 160cc and PowerTorque engines. Also has a section on edgers, Victa-Vac and chassis components from c 1955 to the early 90's.
See if your local library has a copy or checkout ebay or fishpond.com.au
Re the "blade disc/plate thing" I generally use a ring spanner and a hammer - one good tap generally breaks it free, but for your own sake make certain the spark plug is disconnected!!!