Yes, you have the W58 which is a mazda block. The old 70's and 80's blocks of the Perkins and Westerbeke 107 and 154 engines were made in the U.K. at Thornycroft. I'm not sure if the 236 was but I believe it was also. Then each manifacturer installed their own marinized parts. Your engine is newer and most likely more of them out there as they are from the Mazda line. Surprised that the British made those things for 40 years. Those old engines went into their black taxi's, lories, farm tractors and every other thing you can stuff a 4 cylinder diesel into.