I've never heard of warped heads and breaking bolts on a Northstar engine...ever...wow.
(but my time and exposure to them has been limited)
I've not personally experienced any problem with the Northstar leading to a complete failure like the hydrolocking of a natural aspirated 3800 Series 2 (again based on my exposure time). The do tend to burn oil as they age, especially the early version (worst being the first in the Allante back in the day)
All Northstar engies are natural aspirated, however they have introduced an SC'd version in the STS-V and XLR-V and there are different versions of the naturally aspirated. The LD8 is the 275 HP version, there is a 300HP version in the older STS (previous gens), the L47 is the 250HP version. I dunno what the new STS-V, XLR-V SC'd is...you get the idea