bore & sleeving a 390 to make a 427

[Big-Foot]

Containing the piston is only 1/2 of what the cylinder walls do. The rest of the story is the containment of the crankshaft since more than 1/2 of the strength of the mainbearing webbing comes from the cylinder walls. Typical rule of thumb stops sleeving at 2 sleeves in a block as long as they don't share the same plane (mainbearing web). And engine hogged out like this will not last long if it is building any sort of real power.
The Hard-Blok just helps stabilize already thin "cast" cylinder walls and will be of little consequnece in terms of supporting the mains.

Just my $.02 worth...