A few years ago I bought an AVL 500 engine from a breakers. A virtually brand new Electra X had been written off in an accident. When the engine arrived on a pallet, the front engine plates and a few inches of front downtube were still bolted to the engine and they had cut the downtube off with a disc cutter. This was because the factory had pushed a bolt through the engine plates, then trapped it with the primary cases which they must have fitted after putting the engine into the bike. It was a bit of a fiddle, but I managed to undo the nut on the other end and knock the bolt head end out as far as it would go and then using a bare hacksaw blade, I just had enough space to cut the bolt head off, using very short strokes of the saw, then I was able to pull out the remaining bolt shank from the timing side. A stud with nuts on either end is the answer here, as a replacement. The hacksaw work may feel like it takes an hour or so, but it will only actually take minutes and is far more convenient than stripping the entire primary side.