Damn, all but 2 screws sheared off due to tin worm, luckily the engine is out of the frame, unluckily the cover refuses to budge 1 iota.
I do have a spare cover, so I got out the slide hammer, 13mm drill and drilled a hole in the cover to accept an L shaped pull tool for the slide hammer.
it was a bitch to shift and i even snapped a bit of the cover off before finally bringing the recaltrient part off the engine.
Having restored bikes and cars before, I know how to get broken/sheared studding out of alloy. I weld on nuts to the protruding screws, the heat loosens the dissimmilar metals and the welded on nut gives something the spanner can use. All the screws came out great, no problem. Took 10 mins to get them out