Salvagable Block?

I just brought home a 400 block with the intentions of building a 451 with a solid roller cam. The cyl bores are standard bore. I was planning on full machine work including lifter bore bushings.

I got two questions.
1 Is this thing worth using? I really only need the block, so it would save me the hassle of finding a 400 out of a motor home or something.

2 What would be the best way to stop further damage? I have a bore hone that I could knock off the heavy rust in the cylinders. And I could get a brake hone to clean the lifter bores. I was going to just spray what is already there with marvel mystery oil and wrap it in plastic for now. When I have a little more time I can bring it to the machine shop and have it baked and checked for cracks. I have to do as little as possible during my mobile home move which should be over in a month or two.

Here are some pics: