Hi Merv,
The photo below is my hardtop. It was built by Homebush Fibreglass to suit the extended Harrison. Since then there has been modifications to ensure it fits correctly. The underneath has been coated with a resin and microscopic balls(can't remember the correct name for them) mixture to thickness of about 2mm thick to act as an insulation.
The back window is what Homebsh fits. If you are going to build one and fit a rear window like the SPF I think there is someone in the club with a mould to manufacture this type of window.
Warren