Guessing is the road to hell, so here is what I actually know: the cylinders is apparently part of a APE set. It reads "900R" in the place where it usually says "738 cc". I got it this way, and i have never removed the sleeves, so I do not know how it looks on the inside, I can just assume from the oil comming out that it has to do with the size of the blocks bore. I have installed the o-rings in the groove between the block and the sleeves, not knowing there was supposed to be a recess there. the groove is around 2 mm wide all the way round.
I can weld the holes shut, but I am worried that the block might get twisted or uneven in the process.