I have a request for a bit of lettering on the frames ahead of grips on several 62-2 Airweight Smiths. If this space is not engravable, option 2 may be side of stainless barrel.
I think it's engravable, but not fixable if you need to debur or repair a slip. Because it's anodized aluminum, there's no easy refinishing as far as I know, so it probably puts it into the high risk category. The way it goes with me is that I can engrave a hundred initials without a problem, but the one time I do it on something plated or anodized, is the one time something goes haywire.
Obviously the stainless barrel would be safer, but probably not as nice a location as the frame.