Hi,
Transgo doesn't make a "shift kit" this article is what I found searching online for tweeks to improve the performance of a st300. I am sure if you gave the article to someone rebuilding a transmission that they could incorporate it.
Also I got my gaskets from Fatsco, and up until yesterday they were unaware thete was 2 different valve body gaskets, even though they had sent me both types, so I believe if you go for this modification get both types so your not left waiting for the correct one.
I have yet to get my car going to see what difference the hole size makes, will let you all know.
Regards,