Those hole sizes are OK on the plate but pretty wimpy for my taste to be honest as far as the 2nd and 3rd clutch feeds... BUT the hole size DIRECTLY depends on what car the trans is going in, gear ratio, engine mods, track times, etc. I would never suggest drilling huge holes in the plate for a car running 13.5s, nor would I use those suggested hole sizes for anything running 12s. You have to keep in mind that the ATSG Green Update manual is NOT a high performance modification book, it is strictly update information and some tips that rebuilders have came up with over the years to help fix problems, NOT to create firm shifts for a modified car!!! All cars react differently to various changes during a rebuild and sometimes you are left experimenting to make the trans survive and work how it should. A few of the holes in your spacer plate pic really arent necessary to drill out. The 2/4 signal and the TCC holes that are marked to .030" arent critical and I have never seen either one plug up. The 2/4 hole has a filter right next to it to prevent debris but some guys like to open those holes up for slightly quicker signal to the solenoids. The TCC hole is something that may not hurt to open up a little but again I have never seen one blocked up and if something that large is plugging a hole then there are other problems to worry about! What i really boils down to is trial and error. Those hole sizes arent much larger than stock so any change is going to minimal but may not even do enough to be noticable other than the clutch feeds which you would likely notice on a completely stock car. It also directly depends on how the pcm was tuned as there is a night and day difference between a stock and modified pcm. As far as sanding the drum for better forward band bite that isnt a bad idea BUT it shouldnt be glazed to start with and if was the forward band was slipping which is not very common to see on these transmissions unless the band is broken or the trans had very poor line pressure and you would see the rest of the trans cooked as well likely. Those drums are very hard to sand so be prepaired to spend a bit of time to make a dent in the finish! They are not smooth brand new and this was likely intentional to aid in bite.
