It's not really a heavy lift. If you don't want to convert NPCs yourself, Necromancer Games came out with a book called "Fifth Edition Foes" that has the dark ones and skulk in it. I replaced the shocker lizards with death dogs, replaced the harpoon spider with a max-hp phase spider with an awakening spell on it.
There are plenty of humanoid (any) NPCs in the 5e Monster Manual, so when you need more powerful goblins in Drakthar's Way, for example, you can take the Spy NPC and add the goblin traits from the DMG for the sneaks, and do the same with the Thug NPC for the wolfriders.
There is a website called "Kobold Fight club" that has an encounter calculator that's very handy when you're putting it all together. Take the CR for an encounter in the SCAP and calculate the XP reward for a "normal" encounter for a party the size of your PC party and the level of the encounter. Then use that XP budget to make an encounter for your party. You'll typically find that the XP budget ranges from easy to hard for your PCs party level, as it should. If your party gets ahead of (or behind) the curve, you can dial it up (or down) as needed. I've been using milestones, so that's a non-issue for my group.
