If the slot in the gear parellels the camshaft and it is on TDC of the firing stroke the rotor should end up pointing at around 4 O clock looking down on the ditributor from the passenger side fender
I try to follow the OE way Mopar index the disrtibutors with # 1 below the front distribuotr cap holdown, positioned around 4 oclock
As already siad you can make the motor run with the slot at 90 degrees to the cam as long as the firing order is starting where the distributor rotor is pointing at that place on the cap where #1 spark plug wire is when #1 is at TDC on the firing stroke
I've seen B,RB and 426 Hemi motors wired a whole bunch of different ways