Thanks Mike, I'll look for a copy. No, no problem removing the head studs - all came out with a little pressure using as pipe wrench.
It's been dismantle the gearbox and transfer case time this week. Gearbox looks fine - very little edge wear on the gears, all nice and clean and looking good. The stripped case has been soaked in caustic solution, externally sand blasted, cleaned and externally primed, ready for re-assembly. New bearings, shims and gaskets should arrive by Mr Fedex tomorrow (no wonder my wife keeps referring to it as the 'mail order jeep'!)
The transfer case was another matter. You know something is amiss when you drop the bottom cover, and it's full of nice sparkly sludge and has a big chunk of chewed-up metal lying in it! On disassembly, the reason for the sparkles became clear: main shaft case hardening is stripping off. Where the chunk of steel came from I have no idea, as all the gears are intact and look almost new. Fortunately, I have the basics of a spare transfer case, a later model with a larger diameter intermediate shaft, with a good main shaft. Front casting, rear casting and main casing are currently in the caustic bath and will be cleaned and painted soon. New bearings, intermediate shaft, thrust washers, gaskets and seals arrive tomorrow.
The first image is the sparkly faces of the thrust washers with bits of case hardening embedded, and that mystery chunk of steel that washed out of the sludge in the bottom pan, along with a bolt!
The second image is the main shaft, showing where the case hardening is stripping off.
Mike