Just a suggestion before you install it. take the top off and silicone around the whole top before you reinstall it. Didnt do that to mine and it ended up leaking around the gasket. Hope this helps

 

As was said, the seal is "normally" splashed rather than submerged...
Since there is no pressure build-up in a 'rag, what MAY happen is a pin-hole or loose seal will show itself easier when you overfill, so it may leak when it otherwise wouldn't, but it is SOOOO much better on the tranny to over fill it than to risk it running "dry gears"...
and the suggestion to remove the shift cover is the easiest way to do it..
just my thoughts after having to pay for rebuilding the 'rag on my previous truck....

 

When I had my 92, I used to pull the shifter and dump 5 quarts of 5w30 Royal Purple down in it

 

aw gee, I just spent a big chunk of cash on a pro rebuild, which is already up in the truck. Is there no gasket on the top?

 

Even my NV5600 gets an extra qt.