Wood is amazingly strong in compression, and those are built to take advantage of the strength. So I wouldn't worry about them failing. Being made of wolmanized wood, they could conceivably outlast metal ones
Depending on what the cost is, If you are any good with tools, it would be a simple thing to make up some custom stands using the threaded adjusters and plates on them, or buy your own:
Scaffold Swivel Jack - Scaffold, Scaffolding from ScaffoldMart
At six inch extension there's something like a 10,00lbs safe working load on them.