From a narrative level - how hard would it be to take some old MERP adventures and adapt them to Adventures in Middle Earth - not mechanically (I know that bit is going to require a total overhaul), just in terms of narrative structure?
Pretty hard, in my opinion. I've got nearly every MERP/Rolemaster module and supplement released, but it's worlds apart from AiME's approach. Let's take some random examples...
Firstly, forget anything based outside the traditional settings of Hobbit and LotR. Sea of Rhun? Warlords of Harad? Court of Ardor? Nope. You'd need to create a bunch of new cultures for all of those (cultures = D&D races). And, because nearly all virtues (virtues = D&D feats) are culture-specific, you'd need to create a bunch of new feats. And armor/weapons. And monsters, because there aren't sand-wyrms and demons-beyond-the-pale and a whole bunch of other stuff appearing in those modules. You could use D&D equivalents, but you have to be careful - remember that the party has no access to magic weapons or spells, and long rests are very hard to come by.
But most DMs love building stuff from the ground up, so this might appeal. I've seen at least one DM adapt an entire Witchking-era Angmar setting, so that's cool if you've got the time.
Speaking of which... AiME is specifically set post-Hobbit / pre-LotR, so you immediately run into problems with MERP's timeline. Sauron is not at Dol Guldur, which is a deserted (?) ruin. Angmar and Arnor (Arthedain, Rhudaur, Cardolan) are already long-fallen. Tharbad is a ruin, Umbar is in decline, Minas Ithil is Minas Morgul, Thieves' Hold doesn't exist, etc.
Also, supplements like Court of Ardor and Southern Mirkwood are problematic due to the assumed power level and capabilities of the protagonists. AiME is a low-power setting. A single werewolf shows up, and it's a multi-adventure campaign-dominating event. Compare this with a bunch of corrupted Noldor lords and their massive citadels and armies, dealing with demons, communicating with magical Tarot cards (shades of
Nine Princes in Amber), and attempting to put out the sun using the jewels of Ungoliant. But enough about the Court of Ardor, which was always one of the stranger entries in the MERP/Rolemaster line.
So, how about some of the more modest modules: Hillmen of the Trollshaws, or Assassins of Dol Amroth, perhaps? Yeah, maybe these could be mined for story ideas. But it's still a tricky business. MERP didn't model the Tolkien feel particularly well, in my opinion. You've got sprawling keyed dungeons, and small hordes of enemies, and treasure chests with x2 PP Multipliers and +15 longswords. It still runs with many of the base D&D assumptions, because that was the style of the time.
Even stripping out the loot and the magic and most of the combat encounters, you have two frequent narrative problems with MERP adventures. Firstly, many of them are quite happy to send the party into mysterious and untraveled locations. It's the classic "explore the unknown" driver from D&D. AiME characters, by contrast, tend to dread the unknown. If you wander into Shadow Lands (e.g. Southern Mirkwood, Mount Gundabad, the Mines of Moria), you're rolling Corruption checks by the bucket-load. Most AiME adventures occur on the fringes of the points-of-light. A journey into unknown areas is rare and very dangerous; you'd want to use these as the spice in your dish, rather than the main course.
Secondly, you'd want to use multiple MERP supplements. In classic D&D style, your typical MERP adventure assumes there is tons of excitement within spitting distance of (say) Bree. An AiME campaign needs a bigger setting than that to use the Journey rules. This is consistent with the flava of The Hobbit and LoTR, which are all about the journey. Most AiME sessions should see the party moving at least 20-50 miles (bearing in mind that the campaign timeline assumes an average of 1 adventure per
year). That's not conducive to grabbing a single MERP module and trying to convert it.
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My preferred approach is to use the official material (which is of outstanding quality), supplemented by re-tooled modules from old Dragon and Dungeon magazines. I specifically look for smaller adventures that are wilderness-based with few combat encounters, at least one notable NPC, and an interesting story hook.
