Thank you for posting that picture. That really helped understand what you are dealing with.
Ah! I see what the issue is. That picture is taking me back to Ricardo Montalbán TV commercials. The Volare and Aspen with rich Corinthian leather!
Your three speed 3799120 wiper motor was used on the F body cars. I just happen to have one that I use as a test mule for my restoration work. Yes, I changed the end connector shell from the black one you have to one on mine that fits an earlier B and E body cars.
There is no female keyed socket that could be used to make an extension harness. The one I have with the late 60’s B body harness was cut out of a bulkhead connector.
Sorry to say, you will need to do some surgery on the motor to replace the splices on the motor before the cable clamp and use shrink tubing. The socket you would need is available or rob from another three speed wiper motor.
The length on the E body harness is 8” from the cable clamp to the connector shell. The one you have is only 4½” long from the cable clamp to the connector shell.
Hope that helps shed some light on what you are dealing with.
Jim
