Two-Bit hit the target squarely. My Terrier #66971 shipped 4-16-1952,
It is a 38/32, pre-model 32, improved I-Frame 1st version, 5-screw.
Another of mine, #57103 shipped likely September 1950, is a post-war transitional with six-screws.
If yours has six-screws, it is a post-war transitional...