Delco Remy distributor cap question

[Flying Undertaker]

Delco-Remy caps without the R would be for 1968 and earlier usage. In 1969 GM came out with the R (resistor) designation. Caps D 308R ( black caps with aluminum contacts ) and D 309R (brown caps with copper contacts) and rotors D 409R (black with E on tip of contact) and various spark plugs with R designation, such as R43 or R43N, etc. Patent pending R were used until the patent office OK'd the R designation as being different from earlier caps, rotors, and spark plugs without the R. Then the patent numbers were imprinted on the caps once approved with R usage.These parts were then used on earlier applications once the earlier parts ran out of stock.

[John Brown]

If you are still looking, here is a NOS D310 cap that has patent pending and the R on it.

https://www.ebay.com/itm/223454312472?

D310 looks just like a D308 but the towers that the plug wires go into are about 1/4 of an inch shorter. I doubt if anyone would be able to tell the difference once it was installed.