There are quite a few ways to repair this sort of damage, I have done a few on old irreplaceable castings. The easiest way is to sleeve it with a stainless steel sleeve if you can find one the correct size, there are many to choose from. Measurements must be exact but chances are you can find one. these are normally used on shafts for seals but they will work on things like this also. use a sealer when installing.
The next way is to use an aluminum filler, let it site for a while till it thickens slightly then use your finger (use a nitrile glove) and wipe it around the inside of the bore without too much build up, it should just fill the damage, leave it 24 hrs then carefully hand sand it with 220 the 400 grit wet and dry.
Coat the O ring with Hylomar M and install.https://www.amazon.com/Hy-Poxy-H-45...mp;psc=1&refRID=NBMEKJCXE41WV70W8ETH
The other way is just to fill the damage with Hylomar, coat the ring with it and install. it will work and does a much better job than any rtv.