Reverse gear issues.
Reverse gears were a problem on early SIII boxes (esp suffix A) due to wear. For suffix A, the reverse gear simply rides on a bushing/shaft (561954 & 591527). The suffix B and later boxes used the "improved" caged needle bearing assembly sold in kit form (FRC1810). You will notice that reverse is a very small gear which multiplies torque and prevents the vehicle from moving too fast in reverse. Reverse gear is simply an "idler gear" which changes the rotation of the transmission power flow. Presumably, they want you to make the hole bigger to improve lubrication for the bearing.
While you have the box apart, it is wise to replace all seals, gaskets and bearings. Take a look at your 1st/2nd gear synchronizer assemblies. They get a lot of wear. Beware the 3 crazy springs with ball - they fly everywhere if you are not careful! Pay careful attention to the 3rd/4th synchronizer assemblies as well. Examine the brass contact area for wear. There should be visible raised ribs. If they are not present, the synchro's are worn. The ribs displace oil on the cones during shifting and ensure the shafts are spinning as the same speed for easy shifting. Check all gears for pitting, chips or galling. They should have a nice consistent wear pattern. Transmissions are precision machines, so make sure everything is scrupulously clean prior to reassembly. Also make sure to check all tolerances to ensure that they are within factory specification. Take your time and don't get frustrated!
------ Follow up post added June 14th, 2015 10:00 PM ------
Unless your reverse gear is very noisy and/or missing teeth, don't mess with it! If the assembly is wobbly and showing excessive wear, that is another story. But I wouldn't drill any holes in your existing gear if it's working OK.