gcmap says 3,451 miles each way.
So you should get:
3,451 MQM each way
$518 MQD
2,588 RDM
Looks like you read the chart and did the math correctly, we are just using different sources for the JFK-LHR distance. I have found gcmap to be extremely reliable with crediting to Delta, usually within ±1 mile.
The RDM number here (five times MQDs) is for a nonelite.
I always use the miles DL states for the flight (if it's not shown during booking, you can usually click on the flight number and find the DL-defined distance, sometimes with one additional click) rather than looking up the great circle numbers, which DL doesn't necessarily use.