I hear you on the Chapmans and yes, I do have a set on the 517 low deck. 380cfm at ~.700 is great but it's the 335 @.500 and the 361 at only .600 that makes them the killer head for 500 cubes.

I've done The Indy -1's and since even full CNC'ed they wouldn't be much ( if any ) 'measurable' bit better than what I already have, I think they would be too small for what I'd want to do with a 572, essentially the same power at 500 rpm lower but with more torque...when the 500 already has all I need.

The 572 B1 I would think would be the next '1 step beyond 'what I have, more flow/volume for a proportional increase in cubes, obviously needing a bigger cam for the extra cubes but would still allow me to pull past 7k. The thing about strokers is once they run out of head the torque noses over at a very fast rate ( all that extra stroke/piston speed and ring drag starts to work against you) since past the torque (VE) peak the crank's rate of acceleration slows and the rings start to act like a brake. ( Also true for all 4cycle motors) That's why I always build for the widest possible torque curve, simply because it's more fun to drive.

The bore/valve centerlines and wedge angles are the key to the B1, if you scale down the port Cc and flow numbers to any comparable Conventional valve placement BBM head, it would still out torque and power it by virtue of the superior cylinder filling and evacuation efficiency. the chamber/valve placement is also generally why the small block makes more power per cube than the conventional big block all else being equal. The B1 design 'evens the playing field' I think