Plastic will be fine, the real stress is on the end connectors - and I'd assume Rich was planning on using the Mato ones?
You won't be able to make common tracks for the HL and Mato, as the sprockets are different widths and the end connectors different sizes (so they won't engage the teeth properly)

I thought the plastic Mato ones were the rubber chevron? I'd like a set of flat rubber pads for an early sherman, I didn't fancy grinding off the chevrons from ~160 track blocks... (Also a set of steel chevron cleat types as well for my DD)