This resistance reading that you've given also indicates that you've had this kit for a while
Haha I have not personally had this for that long, but I purchased it a while back from a Redditor who had not ever found the time to build it so he sold it to me for a really good deal. It is a Crack 1.0 from what I'm told.
This will happen if the resistor at the headphone jack and the 3K resistor are somehow in parallel. Is there a connection somehow between terminals 6 and 7?
If you attempt to measure the 2.49K resistors themselves, what do they read?
I checked terminals 6 and 7 and did not see anything that would have caused a problem. You mentioned to measure the 2.49K resistors, so I did and they read 1.2K. From you saying the bit about them being in parallel, I looked around and found that the inbound Tip and Ring terminals on the headphone jack had a drip of solder connecting them, so I cleaned it up and the resistances now check out.
The 0Ω on the RCA jack is usually caused by a solder blob or other conductive material bridging the center pin and the ground tab.
There was a blob of solder that I needed to clean up, so I did and now it measures as it should.
Thanks again to both of you for the help! I just finished the resistance check and then moved on to the voltage checks and everything is as it should be so the only thing left to do is plug in my headphones and see how it sounds! I am very excited!