On my 745 box and pistol, noted above, serial number TFJ5492, adjustable sight, wood stocks, has on the box label '7450' as the model number, with product code 103906 and Spec Ord 0229. There is, in the top left corner of the label, above the Model No, the digits 900. Model 745 is rollmarked on the frame.
As far as factory letters, Roy Jinks is on vacation in Italy now, wreaking havoc on fine wine stores and tearing the covers off of golf balls and won't be doing letters until June. For those who haven't seen this news in other sections, it appears that the factory is getting out of the historical letters business and they will be done, if at all, by the Smith & Wesson Historical Foundation. More news will be posted as this change shakes out.