Big inline 6 turbo-diesel
http://cumminsengines.com/uploads/docs/4971109.pdf
Realistically you wont find plans for the full size engine let alone a model one. Best bet would probably be to design your own inline 6 for the application at hand. Engines don't perfectly scale in size all the time, certainly not with a size change this drastic. There would be no guarantee that the cummins when scaled to the size you need would even function. I certainly haven't seen any turbochargers actually functioning at this size so there is 1 modification that needs making right away.
Now right now I have zero machining experience (well, unless you count loading an industrial CNC mill that had already been setup for me) so my advice won't necessarily be the best advice on offer here, but if it was me I'd be going for a plain 4 stroke gasoline/petrol engine. Or if actual power is required then maybe a uniflow 2 stroke with blower.
Certainly no beginners project.
I do personally have my own engine I'd like to some day work towards. Need to get a workshop then practise my machining skills and then work through a few smaller engine projects before tackling my 6 cylinder monster.
