I would buy many gallons of the evaporust and find a plactic bin just big enough for the block. Line the bin with heavy plastic sheeting to reduce the amount of volume you need to fill with the fluid. Find a outdoor pool heater and put that in to get it up to around 85 degrees. Let it soak.
Remember the rusted 455 crankshaft I found for the Gramma car engine build?
https://www.yenko.net/forum/showthre...aporust&page=7