The cowl is off center by 1/8 in. and I can live with that since I got clearance around the valve covers and they're not touching the cowl.

My holes were definetely drilled too far back, as I stated, in my airplane the distance from the firewall to the front of the thrust washer was 6 5/8 in. At this distance (never mind adding another 1/8 in.) using the stock mount and with the engine all the way forward I still wouldn't have cleared the front of the cowl unless I used the wood blocks.