Pretty sure you can just rotate everything so the timing marks line up at TDC.
To avoid any valves hitting pistons etc, before rotating the engine, I'd take the rocker shaft off and remove your glowplugs.
Put the locating pin in the flywheel casing and ensure the camshaft lines up with the mark on the crankshaft pulley.
Pump Timing pin should also drop straight into pump at the timing position.
All this assumes nothing got broke when the belt snapped. If you are very lucky it should all go back together and you will just have a bent pushrod or two.
Mark