Aceman
I am your doctor of love!
Can you please mention which albums/songs you mean? IMHO any of those band's sound has changed a lot over the years.
Edit: Every tome I look for a demo comparison on YT it is al about cranked high gain amps with TS infront, it is hard to notice any difference other that the big bass as described by ACE. I don't use overdrive pedals at all and I like to roll the volume for tone versatility so a pickup that can push the amp hard and then back the volume is something I really like.
Not really...just that Custom is softer/classic while th Distortion is harder/harsher....but Hysteria, Number of the Beast vs Screaming, Ride the Lightning. I'm super-generalizing there. Also - I have used both clean, the Distortion quite a bit.
If cleaning up is your thing, I'd go with a 59/Custom Hybrid.
The Custom clean sup better (and without a 50's wiring mod and a little down turn on the volume, you get to that Iron Maiden place). The Distortion is good for like Biddy Guy stinging Chicago Blues actually, from a Humbucker, but really works best swathed in reverb and chorus. It does clean OK at best. When in Reverb/Chorus soup....Neither are great "for Clean" tools IMO. But they will both push!