@Troble is right, the achiote paste is fundamental to this dish and to other Mexican cooking. You use heroic amounts of it just to make this sauce so don't be daunted by the amount that he has sent you. There is a saying that The Husband and I have - what you are seeking is usually within 5 miles of where you are. I would bet you a lot of money that there is someone in Australia importing (or growing) and selling authentic Mexican chillies. Worth trying to find them to make this dish authentic.
The instructions, as I copied them down from the video, are:
Adobo sauce
toast guallijo peppers, chipotles 2 oz of each
take off ends and shake seeds out
break up and put back in pan, cover with water
simmer for 5 minutes to rehydrate the peppers
lift out of liquid and into food processor/blender
add half white onion, 1oz of mexican sugar, 1Tbsp cumin, mex oregano, thyme 1 tsp all spice 2 Tbsp apple cider vinegar, 2 cloves garlic, pineapple and orange juices about half a cup, 1tsp salt
Blend
Marinade for al pastor
achiote paste 14oz. mash up
add half cup apple cider vinegar, same olive oil whisk
add 2 cups or more of adobo sauce whisk