If your casting is ali, and small-ish, then you will probably find that building up with (TIG) won't be the experience you expect from steel.
Ali welding on small parts doesn't go so well due to the thermal transfer issues – namely aluminium transfers heat too well – and castings tend to be a little disappointing on the material front. YMMV
You would probably do well considering some form of other solution – if it's out of center perhaps you could sleeve it and re-bore …
I know it seems logical to just overfill with ali and fix from there – but even (really) good ali welders struggle with that … due to the nature of the material.
I've been there and got the t-shirt … and watched much better ali welders and I fail in similar circumstances.