BHG
head torque is one issue with the inline six of that era but another major flaw is the bolt design
there are only 4 bolts around each cylinder and if you look at most other engines you'll see 5 bolts around the cylinder .
less bolts means more distance between bolts and less ability to keep pressure constant between the bolts
bolts should be replaced with studs
just replacing the head gasket with a metal one is not gonna cure the problem you need to surface the head and block to finer than even a machine can smooth it out
have a look at some of my bhg shots
http://www.ddmcse.com/turbo/bhg_2003.htm