Does he mean you can hear the water flowing round the heater matrix? If so, I wouldn't worry about it. I've got 2 Sierra twincams and a saph cossie and they all make the same noise (if we're both talking about the same thing that is!! ) and there is nothing with the headgaskets on those (well, the saph ain't got an engine at the mo but that's another story!)

As for alternative engines, how about a Vauxhall C20XE or C20LET??

They've been fitted in mk1 and mk2 Escorts, cortinas etc, so why not a Sierra?