Even if the flywheel is somewhat rusty, the embossed '-0' will be visible on the flywheel. (OK, the dash is below the '0' not on the side, but that's what's available on my keyboard.) If you line up the crank with the marks by the front, then the flywheel mark should be easy to find.
An alternative would be to pull the glowplug on cylinder #1 and use some kind of probe to find where the piston is at TDC.
That said, sometimes it is hard to find. I've spent quite a bit of time myself in trying to find the TDC mark. On my own cars, when I need to mess with it, I try and use some white paint close to the mark on each side, with some kind of slope or other pointy pattern to help me find it next time. Anything will work: nail polish, whiteout - just something that will provide a good contrast for the next time you have a timing problem.
At this point, since you've already set things, you should be able to line up the cam to TDC, then check the injection pump and crank. Since it runs, the injection pump should be very close to the cam. The crank should also be within a couple of flywheel teeth. If it is very far out, you run the risk of bumping valves.
If you have a set of timing belt tools, this is a piece of cake. If not, then find a set before attempting a correction. You will save yourself lots of time and headaches if you get the tools first. Seriously, they are well worth the expense. They will pay for themselves with just this one use.
Cheers,
PH