I expect the governor would be different for starters. Without the serial number reference, you won't always get on the right side of any improvements and modifications even to the basic engine.
Look one up on the CAT literature site and call and see what you can get a real nice copy for before you spend much on it.
http://www.cat.com/cda/layout?m=90800&x=7
There's a couple guys on these boards that have a D3400 generator set, so maybe it will be "trade goods"
D2-5J's, D6-9U's, D318 and D333 power units, 12E-99E grader, 922B & 944A wheel loaders, D330C generator set, DW20 water tanker and a bunch of Jersey cows to take care of in my spare time😄