Hi Gary,
I guarantee it's not an I frame.
Believe me, there were no I frame 38 specials ever made. A 38 special
will not even fit in the I frame cyl window with any bullet but a semi-wad cutter. Although one would not have to see your Centennial to know it's a J frame because there were no Centennial models made on the I frame or the Baby J frame. And the lead pipe cinch indicator that yours has the Model of 1953 size New J frame, not a Baby J, is the large egg shaped trigger guard.
And frame size cannot be determined by grip frame size: Pre 1953 I and J frames both have the same size grip frames while post 1953 I and J frames both have larger grip frames of the same size.
Mistaking the difference between the Model of 1953 larger trigger guard New I frame with the Mod of 1953 New J frame is very common, and difficult to "see" without a side by side comparison. This will help you discern the difference and compare to yours:
This photo is a comparison of a .22/32 Kit Gun "J-Frame" (Model 63 stainless Kit Gun, top), and a Model of 1953 "New I-Frame" 22/32 Kit Gun, bottom). Same size trigger guards and grip frames, but note the 1/8” difference in frame length in front of the trigger guard and top strap, also compare the cylinder length and cyl window length.
Here's another comparison. Top gun is an I frame, with small grip frame, same size as the Baby J grip frame. Bottom Gun is a Model of 1953 "New I frame" with the New frame forging trigger guard size and round butt 1/8" longer grip frame length, the same as yours and the New J grip frame. Compare the amount of un-checkered wood below the checkering field on the stocks.
Your 4 digit serial number indicates 1952 production, the very 1st year.