After Communicating with parts departments for a couple of weeks. one came up with the following idea.
The F3 denotes the MB300 chassis
The 0 denotes left over from last stock run at Warren.
Seeing as as the last stock run was actually 1974 the 74 parts are probably the correct ones.
This idea sounded very logical to me but no way of checking it out.
Any ideas guys.
There are generally three vehicle info tags. The one I think you are using,the 6th digit from the left should be "9". The weight capacities should be on a laminated tag on the driver door post.