On 351C the heater return goes into the block, unlike most where it screws into the manifold. On my 351C the heater connection pipe has rotted off level with the block face. My usual suppliers, CJP and NPD, do not list a pipe connection specifically for the 351C, all are implied as screwing into the manifold. Are these connectors interchangeable or is there a connector specific for the 351C only ? Please help.
Also, on my block there is no evidence of a hexagon portion implying that the last pipe was an interference fit. Could this have been the original fitment or a previuos owner's bodge?

 

These are typically press fit and available here:
http://www.alexsparts.com/products.php?product=WATER-BYPASS-TUBE%2C-NIPPLE-SBF%2C-BBF%2C-351C%2C-351{47}400M-%26-FE