With distributor gear? That isn't part of the primary drive, it's part of the camshaft. There are two types of front end and cam for the Rover V8. Early cars, like ours, have a short prmary drive casing, and the distributor and oil pump are driven directly from the cam. Later, "Serpentine", engines have a much deeper casing with no distributor/oil pump drive on the cam. But the chain and sprockets are common to both types. You really want to buy a "duplex", ie double row, chain with steel sprockets. You can also get these with or without a vernier adjustment for getting the cam timing absolutely spot on. If changing the cam, you need to buy both cam and a new set of followers (The old followers will have absorbed hardened metal from the old cam and will destroy the new one in no time flat). A bit of an opportunity to buy an upgraded cam - there's really a choice of three unless you want to make your engine into a temperemental race engine. Try Rover 3.9 cam (ie suitable for the early range Rover Classic 3.9, not a later Serpentine 4.0), RPi/Piper RP4 or Real Steel "stump puller".
Chris