Long shot schematic request - Grampian 636 Reverberation Unit

Hi folks

I'm staring at one of these units, which a mate of mine has given to me to have a look at and hopefully get back up and running.

Before I disappear too far into the bowels of this thing, I'm wondering if anyone out there happens to have the schematic for it stashed away in their collection?  It's a long shot as this unit appears to be fairly unknown.

Here's a pic of it, if this helps to trigger any memories:



Here's hoping!