I commissioned Smax Smith to build me a 400 horse smallblock.
He used this block, which has had a braze repair done between the two centre cylinders.
After a few hundred miles it must have expanded/contracted and slowly let go.
Eventually leading to a water leak and the mill hydrolocking.
The engine has a well documented list (on here a few years ago) of disgraceful bodges.
(and it only made 230bhp on a rolling road)
I'd say that horizontal crack would just open straight back up as the torqued down head bolts may 'pull' that weak spot apart !?
My block went to a Wild Bunch drag team who didnt need coolant in it