340 block with NO main caps

we used to bury blocks for a yr or so and let them cycle thru the seasons.
I also lived in the Calf High desert, where nothing would rust, ever! because there was never any rain/moisture...so it was ideal for such things.
It does season them, and removes any future core shift concerns. A quick clean up was all that was normally needed.
Sorry, but that block the OP is showing is going to need alot more than that, its been exposed to the elements, not buried for seasoning. big difference....cost in VS value out - simply isnt there, less you own your own machine shop.