Right, so here we are...
Having a look through the Battle Companies Gondor list, I've come up with the following...
Arnor Influence Table (D6)
1 - No reinforcements
2 - Warrior of Arnor with Bow (use stats for Warrior of Gondor with Bow)
3 - Warrior of Arnor with Spear and Shield
4 - Ranger of Arnor
5 - Choose
6 - Roll again on table below
1 to 3 - Royal Guard of Fornost (Use stats for Citadel Guard of Gondor)
4 to 6 - Knight of Arnor (Use stats for Knight of Gondor)
Arnor Promotion Table
Warrior of Arnor with Bow - Ranger of Arnor
Warrior of Arnor - Citadel Guard of Arnor
Warrior of Arnor - Knight of Arnor
Rangers of Arnor can only be promoted if they achieve Hero status and should be replaced with a Ranger of the North model...
There are several selections outside of the official lists, but then the whole Arnor force was left out by GW and this adds the possibility of variety. The Warriors with bows and Royal Guard will be metal Warriors of Numenor with the tree emblems removed. For Knights I would probably move completely outside of the GW range and use Perry Normans with conversions to make them blend in better. Gondor Knight would be fine too with modifications to the shield, but I'm currently using all metal models so I'll probably stick with that. It's not perfect, but it works for solo games. The Equipment and Advance tables will stay the same as for Gondor.
For a larger force, I'm looking at two units of Warriors of Arnor and one of Rangers of Arnor with suitable Heroes to make a 500-600 point force. With the addition of Elladan and Elrohir and an extra Ranger of the North or two it will be easy to escalate to 750-1000 points! I can always add more points with allies from the Shire, Rivendell, and the Grey Havens...
But first, on to Angmar!