I asked Moroso where the indexing washer should go and they said to remove the existing seal washer and install the indexing washer first. Then put the sealing washer on second which allows the sealing washer to do it's job.
I found this picture on the net which shows the opposite which would not seal very well.


1970 YO7 A66 [Canadian Export] F8 Challenger
340 (Currently in shop for stroker assy.)