After all the reading and discussion I think the best path to a Modern Medieval Ale would be Maris Otter with 5% - 6% brown malt or pale chocolate malt. My LHBS doesn't have brown at the moment, but I think it would be a better fit than the pale chocolate if it comes in stock.
Mash temp and pH would be toward the low end to keep it fairly dry, and ABV of around 5 - 6%. I would boil the wort, but only long enough to secure the hot break; perhaps 30 minutes or so. Cooling as normal.
Not sure which way to go on yeast... something earthy or neutral, but not fruity. The most authentic would be a blend of English ale yeasts (they didn't have pure strains by any means) but would need to include wild strains, too. Prolly not available these days...