That's kewl. As long as it works, great.
Double check to make sure your guitar is coming out on both channels.
One risk you run by replacing mono connections with stereo ones is that you'll only get either the left or right channel working.
Weird that ya couldn't find the right plug though. I've got a whole bunch of em sitting around. Come to think of it though, I didn't buy em at Radio Shack, I got em from an audio store I used to work at like, 10 years ago... can't remember the manufacturer though.