It may not be the "correct" way to do it, but you're in a hurry. I would find a 300hp Lta10, and use your injection pump and injectors out of the old engine. You could use your turbo also. You may have a damaged injector from the piston going bad. - Quick and dirty would be to just use your injector pump, and use the rest of the used motor the way it is. It may not run the way its supposed to, but it will run.
For piping and less changing, make sure you find one with the same aftercooling you have, air to air or air to water. Otherwise you will have to take all that stuff off of your old engine.
Adelman's has several different l-10's on the shelf. Something like this maybe? They show both high flow and low flow coolant versions, I'm betting that you are high flow. They also show internal and external balanced versions, and I have no idea what your's is.
http://www.adelmans.com/cummins-l10-310hp-diesel-engine-34669674
The right way is to get all the correct stuff to your cpl, but I find cummins to be less than helpful with any of the older stuff. If it was me, I'd mix and match what I needed to get it running, and sort out the rest later if I had to.