The only way to check is ask someone that has an ls/gsr tranny(someone was selling an ls ys1 in the for sale ask them, or if they never used it ask them to ask whoever they sell it to) and knows which one they have on the same vehicle, and tell you their speed in a certain gear at a certain rpm.
As in 55 mph in 5th at 3000. Then compare yours. If it's the same speed then it's the same tranny as they have and they should know. If it's lower it's an ls(has longer gears), if it's higher it's a gsr(has shorter gears).
This is the only way to check if you don't want to take it apart, or you could call honda and give them the code. They might be able to help.