I hope this will work or at least give you a good starting point. Hard to know what you had in SD--there are many approaches.
Fattier pork is usually used for stewed dishes like this so it is important to watch and not overcook the loin.
12 Californias
8 guajillos
2 chipotles
6 cloves garlic, unpeeled
1 med-large onion (preferably white)
1 t Mexican oregano
1/4 t thyme
~ 1/8 t ground cumin
a few turns of the back peppermill
1.5 c chicken stock
2 T olive oil
salt
sugar
cider vinegar
For serving:
corn tortillas
cilantro (washed, dried and chopped just before serving)
white onion (from above; diced just before serving)
lime sections
Bring a kettle of ~3 c water to a boil. Heat a large dry skillet or griddle (preferably cast iron) over med heat. Meanwhile, stem, split and seed the chilies.
When the pan is hot, toast the chilies by placing several at a time in the pan, stirring/tossing frequently and, once or twice, briefly pressing with a spatula then immediately flipping, till fragrant and lightly toasted. Remove to heatproof bowl and repeat with the remaining chilies, removing them to the bowl when toasted. Cover the chilies with boiling water, weighting the chilies if necessary with a smaller diameter bowl to submerge them, then covering the whole thing with plastic wrap. Allow the chilies to rehydrate, about 30-40 min.
While the chilies are soaking, toast/roast the unpeeled garlic cloves in the same pan, turning often, till the skins are browned, even charred in spots, and the garlic is fragrant, 8-12 min. Remove to cool on the counter. Take two, 1/4-inch slices out of the middle of the onion (simply cut the onion in half on its equator, then take a 1/4-inch slice from each half); wrap and fridge the remaining onion. Char the onion slices in the same pan by placing in the pan and leaving alone for a few minutes before flipping to char the other sides. (You're looking for browned and blacked here and there.)
Remove the onions to a blender. Peel the garlic cloves and add them as well. Save about 1/2 c of the pepper soaking water, drain the peppers, then add them to the blender along with 1/4 c of the reserved soaking water, about 1/3 c of the chicken stock, the oregano, thyme, pepper and cumin. Puree till very smooth. (If necessary, add a little more of the soaking water, a T at a time, to facilitate blending.) Force the puree through a not-too-fine sieve into a bowl.
Heat the oil in a sauce pot over med-high heat. When the oil is very hot, add all the puree all at once (it will spatter!) and stir. Cook, stirring frequently, till its thicker (reduced by about 1/4-1/3), about 5 min. Add the rest of the stock, stirring, then simmer about 10-15 min. Add salt to taste and sugar to taste ( probably ~1 t). Stir in the vinegar to taste (probably ~1 T). Cool the sauce.
Marinate your prepped pork 8-12 hours in the sauce, turning occasionally.
Place the pork in a pan with the sauce. You can cook in your cooker or the oven 275-325. You can start uncovered then cover later, tightly, or tightly cover at the beginning. Turn the meat once during cooking. I'd recommend not going much past 155 since it's loin.
Rest the pork alone, tented, about 10 min. Skim any fat from the pan or just stir it in. Adjust thickness by reducing a little or by adding stock or water. Adjust salt. Chop the reserved onion; wash, dry, chop the cilantro. Flame-toast the corn tortillas to soften (or use a dry or oiled pan); stack and wrap in a towel to keep warm. Slice the pork and serve with the sauce, tortillas, onion, cilantro and lime.