Stumped again

This engine is doomed. found 3 snapped bolts, snapped exhaust lug, cracked exhaust lug on number 2 cylinder. After un-doing 19 cyclinder head bolt, the 20th snapped!....so nearly giving up manged to drill a small hole into the remaining bolt head which is atleast 15 mm inside the cyclinder block. Now got to buy a reverse threaded extractor tool. It may all be wasted if as I suspect that done some damage. So a wasted weekend, donor engine may be needed.