Based on the serial number, your SP would be a second year model from 1990 and would be a short frame.
When the SP was originally introduced, it was built for the 38 Special. It didn't take long for gun writers and other experimenters to rechamber it to 357 and find that it was indeed strong enough to handle the mightier cartridge. Except for one thing....
It was too short to handle the full length of 357 cartridges loaded with heavier bullets, i.e. the standard 158 gr rounds. So some of the early short frames in 357 had the warning to use 125gr or less 357Mag ammo. Once Ruger was convinced the gun was capable of handling the 357Mag, and recognizing the potential market, he retooled to lengthen the frame window and cylinder the necessary 0.10" to accommodate all 357 ammo. I'm not exactly sure when that was, but I would suspect sometime around 1992.
This article gives a little background on the story:
http://findarticles.com/p/articles/mi_m0BQY/is_8_53/ai_n19313632/
I believe they all take the same grips. That part didn't change.