Thanks for the replies. I must admit, the more I'm working on this project and the more advice I get, the more I realize the actual complexity of making a v-block.
I think I should have the block surface grinded, after I've squared it, just to get it 100% true, or as close to that as possible. It should also have much better finished surfaces, I guess? Something that I did notice, and which bothers me somewhat, is that the milled surfaces are very slightly concave in thew middle. If I lay my machinist square over them, I slight bit of lights filters through right in the middle, along the length of the milled surfaces.
I though about doing a longer workpiece and then splitting it in two afterwards and it could probably still be done, as this block is 70mm long.