I've been running a half fill on the 440 in my Roadrunner for 15 years. No issues to date.

Spoke with Mike Janis yesterday and dropped off the block. I have main studs already and I'm going with an aluminum cap. Not sure on the fill yet. Going to try to make this one last so any cam change will be just to use the same grind if this one is damaged.

I have lots of experience running aluminum main caps on stock BB Mopars. I like them if you want to run steel rods. If you are willing to run aluminum rods, then ductile or steel main caps are the way I would go.

I would still inspect aluminum caps for cracks at every rebuild/freshen-up. A very close look can catch a crack before it goes all the way through. And I even found cast iron caps cracked in half at an inspection before the block let go. Set an inspection interval (maybe 2 years or 500 passes?)