Two options might be 'stitching' the cracks, where you drill a small hole, thread it, install a plug, then move half way oaver (overlapping) and repeat the procedure. Very tedious and timee consuming. The other option might be to vee out the cracks (shallow) and solder them shut. I have a continental in an Oliver combine that was repaired this way over 35 years ago and is still in modest use. If you are referring also to an internal crack between sleeves, that one would best be left to a pro to weld.    *( get more than my opinion)   good luck!!