No transfer slot visible means the t-slot isn't flowing at idle. So it'll take time to get flowing as you crack open the throttle. This results in an off-idle sag or stumble. You can partially cover it up with enough pump squirt. I suppose with a loose enough converter it won't be noticeable either. It definitely is with a four-speed and a lot of cam.

Also, with any kind of bigger cam, there may not be enough air coming through with the throttles closed that far. You can also cover that up by cracking the secondaries...

Of course if all you're interested in is idle and WOT on the strip, it's no problem! But there's a lot more tuning involved to have good tip-in and cruise manners on the street. May I recommend the RFS Holley forum.