In a no stress area here's my humble opinion on what I'd do (not that I have)
Two words.
JB Weld.
Mix diligently using weight as the measureing "cup"
Apply to both Inside & out of block making sure to get the gap of the crack
as well as possible, grind smooth. Use your drill hole idea, I liked that.
Repeat. Hey, it works on shampoos!
Get AAA Plus, run it for all its worth and start saving your change for a
new long block or a conversion down the road. @159k it not far off anyway.
The important aspect for sealing the head is to get that mating surface as
even/flat as you can get it from what I've heard.
Later,

Dave C.
Williamsburg, VA
           zzzzzzzzzz__
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'85 GL Westy (His)
'91 Cabriolet (Hers)