If you decide to drill and tap the foot, please use one of these instead:
Rivet Nut
This is a pack of 30 but I'm sure you can find just one or two at any local hardware store. They are fairly common things.
The lens foot is made of cast aluminum and is very soft and "crumbly". Even if you manage to get it threaded 1/4X20, I would never trust it to hold a screw.
I did this on a Sigma lens foot and the lens foot on my Nikon 200-500. Drill the appropriate size hole for the outside diameter of the rivet nut. I think it was 5/16 but can't remember, a caliper or ruler will tell you.
Test fit the thickness since you may have to file a little off as the rivet nut may be longer than the thickness of the foot. It was that way with the Sigma lens but on the Nikon lens it was fine. Do this before gluing it in if you can otherwise you will probably scratch the lens foot when you file it already installed.
I then mixed up some epoxy, applied the epoxy to the nut and inserted it into the hole drilled. If you notice, the rivet nut has a wider flat area, that goes between the lens foot and the lens (or opposite the direction where force will be applied).
Once the epoxy cured and everything was set, I used a little black paint to blend everything together. Honestly, it looks just like the factory tripod mount hole when all done,.
This is the type of use these things are made for (well that and wood working where you want to bolt things like shelves etc.). Bottom line, these work very well where trying to thread cast aluminum will not work well.
Hope this helps.