I have a 1966/67 S2A with the "acorn nuts" style distributor cap. Can anybody tell me if the slightly later (engine suffix D onwards, according to the FWD catalogue) distributor cap with push fit connectors is a direct replacement? Or do I need an entire new distributor to use "modern" HT leads?

Edit:
I've just found a guy on eBay selling push-on HT lead style distributor caps for the early (up to engine suffix C) engines. From this I would reason that the early and later style caps are not interchangeable, but both push fit and acorn style caps can be sourced for the early engines....... Yes?