This is not hard. Call me if you have any questions at all.
1. Remove old driver
2. Sand holes flat with cabinet face and fill with wood putty or silicone.
3.  Enlarge the hole enough so the 126 drops in and the flange sits flush.....it should drop in and have a small amount of "wiggle room",but don't over do it! I use an air grinder. A rasp will work. The hole only needs a little bit of enlargement.

4. Cut the basket damping material as shown in image, the little piece into 5 and roll the big one into a "snake"
5.  Apply to basket as shown, "snake" to the junction of the basket and magnet, each little piece to an arm. press firmly in place.
6.  Set the driver in place and mark the holes, be sure to get it "straight".
7.  Drill a 5/32 hole if you want to use the Hex head bolts.....otherwise dill a very small hole as a pilot hole for the wood screws. Vacuum out all dust.
8. Solder the wires to the drivers....OBSERVE POLARITY! Don't forget the gasket! It will stretch over the driver if you forgot to put it on before you soldered the wires!
9.  Set the drivers in place and screw them down.....the hex screws directly into the 5/32 holes or the wood screws into the pilot holes, either method is OK.
10.  Have a cold one and listen.

Madisound has the K312 Fostex grills. They come with a very nice gasket. It is a good idea to get them for the gasket alone. It's MUCH better than the gasket that is supplied with the driver.