The rocker arm ratio affects the motor from idle to peak RPM, do the math on how much increase in the net valve lift and then decide if you want more lift on the lobes or do it with the increase rocker arm ratio 1.5 X.420=.630 gross lift,1.6X=.672. I check the net lift at the retainers and it had closer to .700 net lift than .670 That cam pulled really hard all the way from a idle to whatever RPM I wanted to shift it at including up to 7800 RPM
That motor exceeded my wildest expectations from day one with a set of ported big valve 906 heads all the way up to buying and using the CNC ported Eddy RPM heads and then with the dyno testing on both the Indy 440-1 and the Indy SR M.W. heads. The SR heads flowed 340 CFM at .700 lift and the 440-1 flowed 370 CFM at .700 lift, the 440 -1 heads made 50 HP more on my pump gas motor at a little higher 7500 RPM than the SR heads did at 7300 RPM More air and fuel in makes more power
I didn't work on the Indy 400-3 intake for either set of the Indy heads, it made good power and torque with all the heads I had on that motor with the same rocker arms with the Eddy RPM and SR heads, same brand and ratio on the 440-1 heads
On the head swap tests I used the same carb with the same jets and ignition timing, head change only, both Indy heads had the same 76.0 CC on the combustion chambers, same head gaskets also
I did test both sets of the Indy heads on my higher compression ratio 526 C.I., 440 mule motor, the 440-1 made 845 HP at 7500 RPM on race gas and the SR made 775 HP at 7500 RPM on pump swill
Good luck on your build, it should make a lot of power