Need information and service manual

[Miles DJ5G KS]

I recently bought a DJ5G Postal Mail Jeep with a (Supposedly) GM 300 inline 6 engine in it. I have seen on other sites that GM made this engine specifically for truck applications, it was never used in any passenger vehicle.
The vehicle is a 1979, but I have no idea what the engine year is, and I am reluctant to start removing and replacing things before I have a book that can guide me through the process.
Does anyone know where I could get information on this engine? It is definitely a GM engine. it is not a Ford 300 inline 6.

 

[66chevyc10]

sure its not a 292? get the casting #s off the block and go from there. don't know of any manuals off hand, but decoding the engine #s should give you a good start.

 

[step1958]

it could be a mopar , dodge, Plymouth, Chrysler, they made a 300 six as well ? depends on the year ?