I have read that quite a few people have used the 1903 from refrigerated trailer units with good success , some have used the 2203 but have to be careful because of the higher power. Machine work can quickly add up , might want to check with fel-pro for gaskets, they are known to make gaskets that solve issues with problem engines.
20 thou over size won't be an issue.
The sleeves these motors run are press fit, they are not wet liners, so there is plenty of support for them not to split.
As long as you can get 20 over pistons, go for it. Adding sleeves is an option, but they aren't cheap. You need to bore the old ones out, press new ones in, then bore the new sleeves as they are not just press in and ou're good to go.
If the pitting was on the deck of the block, just take what is needed as long as they don't touch the area tha the injector pump sits as that adjusts fuel timing. Your machine shop then takes the required amount from the top of the pistons to ensure the piston to head height is right. Your machine shop will know all this and have the gear to do it.
