On a previous post, JD mentioned the recessed nozzle block on early 375 units and Jim Lockwood posted a nice picture of one. I have an early unit (#1449) which does not have them so I have been doing some research. In Noland's book, page 133 has a prototype picture (no flags on lid - only a single snowflake) without the recessed boss. On page 139 he states "The last fuel-injection unit reporting the "nozzle base recess" is number 1908." Although I have only had my unit a few years, I know the history back over 30 and do not think the plenum (or tag) was changed. See the attached pictures, the unit was very rough when I got it. My question is did some early units have the recess and others didn't? Don H. ID tag as received.jpgnozzle mounted.jpg