I have a sleeve in my 68 YZ block and you'd never know.

The pitting between the bore is going to be a big challenge to keep sealed. Hope with milling the block you get most of that to go away. You might consider a graphite head gasket over the standard fiber reinforced versions for better sealing properties. I would opt for a wire ringed head gasket as well for higher sealing pressure around the bore. Don't use the Multi layered steel versions unless your surface finish very very very smooth.