Ideal? I don't think there is one. But you should be able to narrow into a profile that worked well with the style. Considering that you can always add sulfate to check the effect in the finished beer, I would aim for the malty profile and possibly spike a glass or two with a bit of gypsum to evaluate if you would have preferred the flavor of a more balanced profile.
Remember that the bicarbonate content in any profile is just a starting point. You will have to adjust that level up or down to suit your grist.
Martin is right. I suppose Lett's (known of course these days as 'Killians") would
have served as a standard for this type of beer ...but since there hasn't been an Irish brewed version since the mid-1950s, it nothing but guesswork. I doubt that the French version introduced in the 1960s was totally faithful to the original recipe, and the American version certainly
isn't especially since the recipe has been reformulated by Coors more than once (except for the very beginning when Coors labeled it as an "ale", it has for most of it's US existence been marketed as a "lager").
Perhaps some research into the character of the water in Enniscorthy where Lett's/Killian's originated (as a true ale) would be a good starting point.
The grist would be anyone's guess...I think if you start with a good, bog standard 'ordinary bitter' and use a small measure of appropriate roasted specialty malts to get the color, you'll wind up with a good beer you can safely call "Irish Red".
Since there is no 'standard', and certainly not very many people around who will be able to compare it to the original, it seems to me that you really can't go too far wrong. Any attempt to define the"style" with a standard
definition is, in my opinion, futile (and like other older "styles", usually based on arbitrary speculation).
I'd be curious as to what Kristen and Pattinson could offer ...'patto',are you listening? In your diligent and peerless research, have you ever encountered any inside info about G.H. Lett's brewery?