Before I start working on the blocks, I want to get ALL the parts clean of all the grime on the outside, oil varnish on the inside, and anything else that's clinging on. I could send it to a shop, but I'm trying to do this on the cheap. Anything I can use at home to clean up all the parts? (Aluminum and steel)
I don't want to affect the tolerances of anything (bearing surfaces, piston bore)
Any ideas?

I just used lots of degreaser and a various stiff nylon brushes. There's nothing very magic about it. $20 and 4 hours.

Make sure you clean out the various passages with some long engine brushes afterward.