I would sight your 30-30 the same way. That should be good for 125-150 yards or so. That way your sight pictyure is the same, but obviously, the 30-30 is not as flat shooting as a .270 Winchester.
You will need to consult factory ballistics charts to see how far you can shoot without holdover, or shoot at 150 and 200 yards to see where it shoots. Sighting in too high often results in overshooting at short range.
If you sight in 1.5 inches high at 100 yards, you will most likely be shooting 3 inches high at 50 yards.