There are plantations of hardwoods that produce sawlogs, for example the NSW Forestry Corporation has just under 35,000 hectares of hardwood plantations for sawlogs, more info via this link https://www.forestrycorporation.com.au/operations/about-our-harvesting-operations/hardwood-timber-plantations.

A 50-year structural design life is required by some authorities, for example James Cook University calls for a minimum "building design working life" of 50 years for its own buildings. Perhaps glulam producers have aligned their warranties to this common requirement. We are not aware of a glulam producer that warrants its products for 120 years. It would seem somewhat impractical given that such a long term warranty could never be exercised. The personnel who issued it would be long gone, and probably the company as well.

The Queensland government website could be relied upon, but for Australian Standards authority AS 1720.2, Timber Structures, Part 2: Timber properties, quotes a density figure of 1,000 kg/m³ for spotted gum at 12% moisture content.

If there are no grade marks on the timber you would need to have a timber grader assess the timber on site in accordance with the relevant Australian Standard. Someone who is experienced in grading timber could do this, for example a person who has completed a visual stress grading course at Timber Training Creswick. The same person may be able to identify the species of timber. Otherwise you could send a sample for identification by an expert such as Dr Jugo Ilic who is an authority on the subject.

Drying timber by dehumidification is a more gentle process than the more conventional kiln drying methods used in large-scale timber production. Consequently dehumidification leads to less checking (a bonus with Australian hardwoods) but the downside is, it is relatively slow. Progress needs to be monitored by testing the timber at intervals with a moisture meter. There is much helpful information on the net about building a dehumidifying kiln, mostly from US sources. You will find this information if you write "building a dehumidification kiln" or similar wording in your browser.

The allowable overhang for an LVL will depend on the size of the member and the load it supports. Maximum overhangs for various load situations are tabulated in the span tables published by suppliers. Span tables can be found on supplier websites, or can be generated using timber design software. A selection of design programs can be found on our website via this link https://www.woodsolutions.com.au/resources/specifications/span-tables-and-software.