Found a reference where it says they retained their old 600 psi boilers.
Still not sure what changes were made to burn distillate fuel but they may still be able to burn the black oil, but would mean they need to take on more oil than with the distillates, which provided better fuel economoy.
the quote is from
http://web.mst.edu/~rogersda/america...attleships.pdf
When the four IOWA Class battleships were re-commissioned between 1982-87, they retained their old 600 psi boilers while switching from Navy Special Fuel Oil to Distillate Fuel.
As to their effectiveness as warships - lets give this quote as to what the Soviets thought of these ships
"You Americans do not realize what formidable warships you have in these four battleships. We have concluded after careful analysis that these magnificent vessels are in fact the most to be feared in your entire naval arsenal. When engaged in combat we could throw everything we have at those ships and all our firepower would just bounce off or be of little effect. Then we are exhausted, we will detect you coming over the horizon and then you will sink us."
-Soviet Fleet Admiral Sergei I. Gorshkov,1985- Quote after watching the Iowa in a NATO exercise