CAN transmit source address

I am trying to transmit a J1939 CAN message that another controller is expecting from a specific source address. I have the info below, but and having trouble setting up the message. My Dewe 43 is acting in place of the ECU.

ECU Address = D5

Dual Channel Processor (DCP) address = 9F

Message Description: Weight

PGN: 61184 (00EF00)

PDU specific = Destination Address

Data length: 8 bytes

Default Priority: 7 (lowest)

Direction: ECU=>DCP

Repetition rate: per drop

Description of each byte of the Weight Message

Bytes    Bits        Parameter

1             8-1         Message type LSB (0xFF)

2             8-1         Message type MSB (0x00)

3             8-1         Weight LSB

4             8-1         Weight

5             8-1         Weight MSB

6             8-1         NA

7             8-1         NA

8             8-1         Weight units (1= 0.1 kilograms) 

How do I set my transmitted message to the ECU source address, or set the Dewe 43 as this address?

The arbitrary ID field only allows 4 digits, yet as I understand my message ID for this should be 7EF9FD5.

In this case I have other messages that I also need to send, also with the same PGN, destination address, source address, and sometimes the same priority level. What am I missing to differentiate between messages?