Don't really know about Holley , but you couldn't give me a gold plated MSD. Seen too many of them fail. A friend of mine lost 2 on his dyno and I think its 5 now on his boat. He also has an engine shop and does boat , drag and roundy round motors. You wouldn't believe the ones that come through there.
Myself...I'd stick with a Merc Thunderbolt.