The Qantas Founders Museum is a must for all visitors to Longreach, not just aviation buffs.

It gives an interesting historical perspective to the founding and early development of this Australian international airline.

It is easy to spend 5-6 hours there, and others reported they had spent similar time.  This includes a short break for lunch.

You should consider doing all the tours - including the Boeing 707 and the so-called Wing-walk on a Boeing 747, which is a bit of a misnomer as it also includes sitting in the cockpit and the cargo holds.

Fairly expensive all-up, about $100, but a very enjoyable and interesting day - and the Museum is a non-profit so the money goes into supporting it.