Big Block Cylinder Heads "915 vs 906"

I used a pair of 915's on my Race car in the 90's.
My machinist told me that they were like a early swirl port type head.
Back them, that was the big thing, swirl port heads, as this was just coming on line with the OEM manufacures.
I didn't have anything on 906's for comparison.
The engine was based off a 440-6V engine, .060 over, balanced, stock rods, stock crank, L2355F pistons, & a 620 lift Crane roller cam.
It would run 10.60's in my Super Street Duster @ 3100LBS.
The heads had the bigger valves, the bowels opened up & the int & exh ports gasket matched.
I thought it ran very well for what it was.
If I had my choice, I would pick the 915 over the 906. I like the closed chamber.