First Classic Ford - Need To Locate Engine Number!!!

Hi guys my name is Jamie, this is my first time on the site and I'm hoping someone can help me out.

I finally bought my first classic ford! I've got a 1966 mk1 Cortina which has a 2.8 v6 from a capri under the bonnet. I bought it off a retired mechanic down south who put it together. He couldnt remember what year etc of capri the engine is out of which is proving a little bit of an issue when it comes to buying parts etc for it.

I'm new to working on cars (apart from standard maintenance) this is my car for learning on. I've had a few problems with it which, along with some new tools and a Heynes manual I've managed to sort. At the minute the car is overheating quite badly when sitting idling, I took it to a specialist who agreed that it might have something to do with the thick rusty water in the radiator/engine block so my project just now is to get the rad and block flushed out and replaced with clean water and anti-freeze before winter. In the process id like to replace the thermostat but as far as I can tell from the Heynes manual i need one that opens between 79 and 83 degrees. All the ones I've found on ebay etc open at 88/89 degrees.

I figured I would try to phone a specialist to get the part but I dont know the year of the engine. So my question is: does anyone know where I can find the engine number or a serial number etc on the engine block that I can use to find the year of the engine???

Any help would be greatly appreciated!!!

Thanks guys