I used these Hi5 replacement linkage plates on my Giant ATX frames for almost a decade. Rear travel went from 3.5" to about 5". With a 130mm front fork it made for a pretty versatile bike. There were several drawbacks: it made the bottom bracket pretty high by modern standards and it gave an already flexy rear end more flex. This was particularly noticeable when going back to this bike after riding my Anthem X.
They were made in Australia by Crash Test Research Pty Limited.
Here's a close-up of the instructions in case anyone ever needs them:
