If the chain has "stretched" the sprockets will be worn as well so ideally a set of sprockets and chain would be required.
The stretch is caused by wear on the bearing between the pin and the roller, result is not all the rollers fit the sprocket grooves. Resulting in all the strain going on a few of the sprocket grooves giving rapid wear to both chain and sprockets.
A quick check: Line up the timing mark on the cam, and see how far beyond TDC the crank ends up. If you end up fitting a new chain, the split link is only used temporarily, to roll the new chain in, turning the crank by hand - you then rivet a solid link in place of the split link before running the engine.