Need help with ingredients for a Korean dish

I picked up the ingredients to make a recipe for sliced pork butt marinated in a Korean spicy paste, but I forgot a couple items – gochugaru and plum liquid.
Can I get away with using regular chili flakes or powder in place of the gochugaru, or will it significantly impact the final result?
The plum “liquid” is optional in this recipe, but I’m not really sure what this is – juice, extract, maesil. Google leaves me more confused. Is there is a reasonable substitute item(s) that I might use to replace it or should I just skip it?

The ingredients:
1 pound thinly sliced butt
2.5 tablespoons gochujang
1 tablespoon gochugaru
3 finely sliced green onions or scallions
1 clove minced garlic
1/2 tablespoons toasted sesame seeds
1 tablespoon rice wine vinegar
1 tablespoon plum liquid (optional)
Black pepper
1/2 tablespoon brown sugar
1/2 onion and 1 pear, pureéd together
1 tablespoon sesame oil
1 tablespoon ginger juice