I think there might be "some" gains to be had by (as Grumpy said in his 1975 SBC book) "fiddling with the cam".
But, the fact that the motor didn't respond at all to a pretty big swing in rocker ratio changes....... I don't think there's any "easy 25hp" to be gleaned from only swapping the cam at this point.

I'd be looking towards the EM builds for inspiration as far as the cam goes.

Btw...... Did you mess with the lash?