Engine codes

Hi all, looking for some help coding a 454. I'm showing the back engine code T14 and 3999289 which I thought was Tawanaka plant, a 1971 or 71 to 74? Another code on the front passenger side reads T0910TRW which shows a Tawanaka plant Sept 10th and a truck engine? I'm trying to put new plugs in which look a little rich and the plugs in it are ACDelco R45ts. Look short because of headers. Any help would be appreciated. Thanks

Codes for TRW as follows:

Code Year CID HP Model Comment
TRW 1974 454 245 Truck LS-4 VIN Z, L, f.d, 20, 30
TRW 1979 454 210 Truck LF-8 VIN S, fwd, 20