Mattias - you didn't tell us the year of your truck, or if it was carbureted or fuel injected.
You see (at least in the USA) carbureted B2600 engines were Mitsubishi-made and later fuel injected B2600i engines were made by Mazda.
Anyway, I have the B2600 factory manual, and it lists for the 1988 Mitsubishi B2600 engine cylinder head bolt torque at 88-98 NM, done while cold.
For the 1991 I have an electronic factory manual, and for the 1991 B2600i engine I've posted a screen capture below. For sure in USA the 1990-1993 B2600i engines were same/extremely similar.
You also might want to visit mazdatrucking.com; there's a guy there who calls himself Axel Breaker Earl who is real knowledgeable on 1986-1993 Mazda engines.