Has anyone ever come across a procedure manual that covers replacing the head gasket on a 1991 240 B 230
In the Oz Volvo Technical Archive. Search for TP30871 which gives basics. More detailed procedures for B21 engines (which are similar) can be found by searching for TP30170.
The head also needs to be put in an oven and heat treated so it's flat.
Merely resurfacing the block face of a head which has overheated doesn't address the fact how it has warped, which will cause camshaft bearing wear.... and then blow the HG again in a short space of time. See https://pbase.com/stealthfti/image/25123315