Can rusty cylinder heads be used?

i saw rusted though holes in a block and head that had been laying on its side in the weather for years . ate a hole that would have showed up after cooking and slot peen rolling it to clean out the passages . had him (my machinist) do that cleaning process to everything now . it does a beautiful job cleans cast iron until it shines . then sonic test for thicknesses thru out . oh and the guys block and head that had the hole in them . well he didn't want to pay for that extra . now not only getting another block and head , he's having to redo the whole assembly again . lucky i guess he's got all new parts to put in it , lol . because the leak only showed up after it was assembled, and going the run to breaking it in .