That "Opportunity Knocks" Engine

[J and M Machine]

Beautiful work J and M!
Is the small circle visible in your photo or does one have to look at a real block with a loupe eyepiece? Is the circle the END of the casting wire and therefore very small? I am interested to know what to look for.
SAJ in NZ

Thank you for your compliment.

You can see it in these pictures as it is the core wire. . If you look close the factory ground it off. They are of centered over the crotch of the cylinders and its prevalent on 1930-31 model engines.
The core wire is steel and over time rots away leaving a void for the water to leak.

 

[100IH]

Stitch it-Irontite pins. Then run their ceramic seal.

 

[dumb person]

Drilling the ends & driving in soft wire or lead should be ideal for prepping it for JB weld.

You could try to solder it with normal electrical solder. Not brazing or even silver solder, i'd consider those 'too hot'.

If you want a better compound than JB weld i hear great things about some product from belzona?
https://www.belzona.com/en/products/1000/1111.aspx