I wanted to know if I have this right.
T1031IF
Tonawanda Oct. 31 (Police) H.D. Clutch
1968 Chevrolet 396

There are 3 uses for IF BB in 65,67 and 68.
You have listed one.
Check here
http://www.nastyz28.com/sbchevy/spcodeb.html

Check the casting number and cast date from top rear. The cast date on some early BB is on the side of the engine(passenger side) next to freeze plugs. (Letter for month and number for day and last digit of year).
Also is there a partial vin on the front pad next to the ID code? The second digit is usually the model year 18B+ for example is
1=Chevy
8=68
B=Baltimore plant
+=car sequence number

Verify BB casting numbers here
http://www.mortec.com/bbc.htm

Rene
66_Malibu

The vin number is 18F139474. So it must be a 1968 engine.