I recently purchased a Kats 11405 (36mm) block heater for my '78 Brat with the EA71.  It is supposed to thread into the hole directly to the right of the crank pulley. Everything I've read and found from Kats says this hole should be 36mm. However, the hole in my block is only 26mm with a plug that's removed with a 14mm hex head socket. Anyone else have any experience with this or know the correct block heater that I should be using?

I'm not sure but check around for an Allen head plug. Maybe on the passenger side.

Thanks moosens, the plug on the passenger side of my block does have an Allen head. There is also one on the drivers side that's blocked by the water pump but it looks like it's the same size. Everything I've found says the plug should be 36 mm but mine is 26mm for some reason?