320 works just fine and is what most people use and suggest, even Transgo over the years. 320 is not very rough and will wear pretty fast, just make sure you are using the wet/dry paper not just regular paper as it works better. I have been using medium grit scotchbrite pads for a number of years and those work very well also and last a lot longer-NOT the roloc pads for a grinder!!!-actual pads you use with your hand. I can see why they suggest drilling the holes in the fd shaft as those bushings are the most common to wear but good fluid and service intervals keep things alive just fine but I always replace the original bushings in this area as they are always worn, but this is on typically 100K+ mile transmissions. As far as the feeds in seperator plate you have to know what you are going and why. What the ATSG update manual suggests is NOT for performance applications and is an attempt to fix problems with sloppy and long shifts. I have been opening up these feeds since the first performance 4T65Es I built back in the 01-02 timeframe and know what sizes work best for what combo. You cant just drill big holes and call it good! I have opened these holes to .140" before but I would never suggest doing that for the everyday driver that isnt making lots of HP. Opening those feeds is no secret to guys that like to dive into the books and understand why they need to be opened, yet other than myself I have not seen a single other performance trans builder open those holes. The other guys like to block accumulators which is not the best way to go about firming up shifts. Sure adding lots of spacers limit or completely block the accumulators but the feed hole is still the same size no matter what you block in the accumulator body. The accumulators are there for a reason and should be left functional. If it is a strip only car then it is one thing, but I doubt there is 1% of this community that has a car that only gets trailered to the track and is never driven in traffic.
Time for some more reading.
