Clean inside matters, not outside. One thing, if it goes into a machine shop, they're going to want to bore it, whether it needs it or not- it's what they do LOL. We'll punch 'er thirty, and .... Cut the crank, needs it or not.... That's why it's nice to check it out first yourself if you can. I really hate to bore a block that doesn't really need it, the walls just get weaker, and that's less times it can be rebuilt in the future. Most shops will just start checking off every box on the work order, line hone, deck, like a race engine. Most production FE's don't need a line hone at rebuild- and there's ways to check- but Chebbies are another story. BTW, if the shop you're going to is a Chebby-happy shop, that's, umm, not good for your FE. Many things you can check yourself, and aren't really necessary for what you're doing, if it's in good shape now. Of my 8 427's, 5 are straight and runable at std.- and most have been run at std several times- including a '63, a '64, a '65, and a pair of '68 side oilers. The other 3 were already bored when I got them LOL
Sounds like your heads have suffered multiple valve jobs- if the guides are still tight, you could probably put in some new seals and run them. If they're that far gone, rebuilding them could get more expensive than they're worth.