Trying to adjust the injector lifters on a d315 in a D4 7u. By looking at the valves, it appears the marks are wrong. When it shows 1&4 it should be 2&3, And when it shows 2&3 it should be 1&4. Would it be possible for someone to have installed the flywheel 180% out? If not, something is really strange. Any help would be greatly appreciated.

The subject of flywheel alinement has been discussed, so it is a possibility. I forget which models it was possible on. Hopefully bring this to the top brings you a better answer.

Yes, The flywheel could have been put on at sometime incorrectly. There is no dowel etc to make it idiot proof to install.  The crankshaft flange and the flywheel have a mark at one of the holes to align the proper bolt hole up. You can't see them unless the flywheel is removed. I guess your best bet is check the valve timing with a dial indicator. That is described in the D315 Serviceman's Reference Book. And see which timing marks align with your flywheel at #1 piston.