magnum hds

'What flow numbers could I expect out of a set of mildly ported Eddy magnums?
What performance gain/loss might I expect from my 388?
Presently:
CI 596hds w/SS202/1.625 11/32 stem ucvalves, 67ccs, ported, gaskt mtched
Calculated 10.7CR
RB cam 264*@.050 I.555/E.520
Airgap w/ 750mighty demon

It runs great up to ±5700rpm and then seems to fall off ie. quit pulling as hard after the 1000' area at the track.

With the magnums the CR goes to 11.9 but aluminum and the cam lift will be the same .555"