Mike,
You will find I frame .38 Terriers in these first four post war categories:
1. Transitional I frames c. 1946, leaf main spring w/strain screw on forestrap: These are "5 screw" models, 6 screws in total counting the strain screw: round sight, small trigger guard and short rd grip frame or rebated frame w/sq butt stocks, (all reportedly have new style hammer block). .22/32s and .32s beginning as low as 5346XX (Two in 521XXX range recorded as shipped in 1948 and 9/49, probably do not have the new style rebound slide operated hammer block reportedly begun at # 536,685), #544030 lowest observed; .38 S&W beginning c. 1948 at # 54475; as high as 582XX w/rd top stocks.
---- a) Pre war/post war trans.: uses pre war parts. (includes the non-Model #’d 1957 issue .32 Regulation Police Targets in the low #657XXX range). A few small guns were sold in the late '40s mostly made up from prewar parts. Actual .38 S&W production in volume didn't resume until about 1950, 54804 lowest and 58470 highest known shipped in July 1951.
---- b) Pure post war trans.: uses new post war parts. .32s (up to #550740 highest # known).
2. "Improved I frames" w/coil main spring: "5 screw" model, (the strain, 6th screw was eliminated), otherwise same features as the above Transitionals. Exception: late issues have ramp front sight and barrel rib. These are not pre models. No .22/32s made in this model, .32s (beginning at #554536, lowest # known shipped 12/51, #611398 highest known), .38s (highest round sight 70XXX [#68,XXX 2/53], lowest known ramp site 70131, 71983 shipped Jan. 12, 1954, highest known 738XX).
3. Model of 1953 New I Frames, (the true “Pre-Model #” guns), coil mainspring: These are "4 screw" & "3 screw" models, larger trigger guard (no screw), longer rd butt grip frame and new style sq butt. Bright blue finishes begin to appear c. 1956 and eventually predominate. .22/32s (beginning in new serial range starting w/#101), .32s (beginning at about #613XXX), .38s (a 4 screw, old hammer #7671X, 71983 shipped Jan. 12, 1954, 80627 highest known, a 3 screw).
4. Model #’d guns c.1957, otherwise identical to the Mod of 1953: 22/32 I frames Models 34 & 35 (beginning c. #37XXX), replaced by J frames Oct. 1960, -1 added (c. #70,XXX), the .32s and .38s in early 1961, -1 added (.32s Models 30 & 31 beginning c. #650XXX to #712954, highest # known, and .38s Models 32 & 33, c. #88XXX).
Recently there was a thread you may enjoy about terriers getting a 38 Spl cyl transplant for the very reason you bring up.
38/32 Terrier to 38spl conversion