Overall length of the Hatori 650 pipe ought to be about 15.5"

Overall length of the Hatori 700 pipe should be about 17.00" (corrected from 18.75" from the Hanno pipe)

Singapore Hobbies description:
650 = TUNED PIPE 60L (LONG)
700 = TUNNED PIPE 10CC (SUPER LONG)

I don't have any 700's...But it should be a great pipe for the LS engines such as the OS 61 RF-P you have listed...

Either pipe should be Awesome...Not sure how this fellow could tell the difference between the 650 and 700 from the photo??

I believe your pipe is a little earlier generation...It's all smooth....I think the later pipes have a different appearance and the baffle welds are visible...

I have a 1987 Hatori catalog which shows your style (all smooth)...Then below is a photo of one of my Hatori 650 pipes which was purchased in the early/mid 90's...

I know of no performance difference between the "smooth" or "crude" versions...

edit: (Update)
Added a photo off an AD I found which actually lists the Hatori 700 closer to 17"...