There are so many rust removal treatments, some of which are available from companies like Eastwood and others supplying rust removal chemicals. Some of these are extremely effective, yet are mild to things like, say, human skin and lungs.
I use an Eastwood rust removal product that does an excellent job, and rinses out with water. However, there are others that are equally as effective or better, that are less irrating to the user, and things like pot metal.
I also have half a dozen oil pans to play with if I want to do a "T" pan with a baffle, or order up a modified pan. Mostly, there is not much rust in an oil pan... And anything on the outside can be taken care of with a wire wheel brush.
You really dont need to use any abrasive blast to remove rust from the pan. As for the block, I have found that a good quality spray or brush on paint stripper works wonders. Check out the pictures of my block prep in my build album at Westyxiownersbuildersdrivers.
Even alloy canstings are easy to fix, with a thorough cleanind and the application of Eastwood "Alumablast" to produce a clean alloy appearance that doesn't flake off. Works wonders on transmission housings and the differential case.