Your distributor cap, or even the new one you purchased, should have the number 1 cylinder location marked on the cap. From that position on the cap, follow the Y block firing order, 1-5-4-8-6-3-7-2 in order COUNTERCLOCKWISE on your cap as you place each corresponding plug wire on the cap. Do not forget that the Y block cylinder numbering begins in sequence with number one cylinder on the passenger side at the radiator (unless you are in the land down under! 
), and that number five will be at the front on the driver side with 8 at the firewalll.