The hammer release either has a single hook or a double. I replaced mine a few months ago. The Tapco trigger is well worth the money and I replaced in about 20 minutes with gloves and needle nose pliers.
I found pictures on the Internet with a Bing search that shows both type sand what they look like. If I recall correctly, a single hook will work in all AK's but double hooks only work on double hook specific AK's.
Mine was a single hook. I took all kinds of pictures and geared up for the worst. It was stupid simple to do other than I had to pull a pin out of order from the instructions to get the safety lever off. The only slight issues I had were the cuts from the spring (hence gloves) and jiggling the shepherds hook back in.