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[nashvillebill]

The anti-drainback is in the front cover itself, not the reservoir. Lifted from a writeup by Chris Nigh (on converting the 94 cover to the later anti-drainback):

Step 5 is to create the new standpipe hole in the timing cover.
To create the new hole in the timing cover to the new reservoir standpipe, I VERY CAREFULLY centered the F6TZ-6619-AA gasket on the timing cover. Center punch the timing cover where the additional hole is using the F6TZ-6619-AA gasket as a template.
At this point you will be making lots of metal shavings so be very careful and prep the area with lots of rags and such protecting any possible path into the engine. I used several layers so that I could remove them one at a time and vacuum very thoroughly between each layer I removed. I also used plenty of brake cleaner to wash the metal particles onto the rags before I removed them.
Drill a 3/16" hole down through the timing cover to the small upper drivers side cavity. Don’t have to be terribly careful other than making sure the hole is perpendicular to the timing cover. I have a buddy stand at the side of the truck and watch the front and back tilt, and I watched the left to right tilt and drilled away. Once that is done, you will need to make the special gasket relief tool, or in other words the 11/16" spade bit with the end tips ground down so that it will create a flat gasket relief in the timing cover. Here is my special tool:
Nigh.org Photo and Video Gallery
With the special new drill bit, create the gasket relief the same way you drilled the hole. Be careful not to drill too deep. Go in steps to make sure that you get the depth right. I used the old gasket as a depth gauge. Here is what I ended up with:
Nigh.org Photo and Video Gallery
Step 6 is to plug the existing hole in the timing cover.
Last part of the mod is to plug the hole in the front of the small cavity. I used a self tapping screw from the REAR of the timing cover coated with lots of RTV. Once it is in place, trim the excess screw that is protruding into the gear area.
Nigh.org Photo and Video Gallery