Where's the iron start? I'm assuming a top flange?
If that's the case, what I'd do is drill and tap the bottom (crankcase side) of the holes, about 1" deep, for a fine thread only a little bit bigger than the new bore size. IE, if you have a 6mm hole now, and need to move it inboard 2mm, bump it up to a 10mm thread.
Turn and thread a chunk of aluminum rod to fit- doesn't have to be a perfect fit- and screw it in with a generous helping of red Loctite.
Once it's cured, saw it off, machine flush, relocate the hole, and drill most of the way through.
If the iron liner has a flange at the top, turn the cylinder over, relocate/reindicate the hole to be drilled at the top, and as noted above, use an endmill to gently drill through, and hopefully down far enough to meet up with the new hole from below.
I think it'll work, without more data, but it's also worth keeping in mind this is not the only way to do it either. For example, you could, assuming there's sufficient meat to the cylinder, drill it oversize, ream, and press in a solid bar of aluminum, with no threads. Then just redrill the new hole location.
It's also possible to plug the holes in the crankcase with threaded slugs as above, and redrill to relocate the studs instead of the cylinder holes.
Always more than one way to skin the proverbial cat.