1974 D300 360 fresh rebuild will not start

That would account for the spark timing to be 180 degrees out but would not account for low compression, is there another dot on the back side of your cam gear? I'm not sure if they can even be installed backward but the timing dot on an OE gear is up on the tooth ring.
That picture isn't quite big enough to see, but I think they were off by a tooth, as well :/