Hi Jrthompson,
Yes, you can drop the SCX20 into your backbone and depending on the data you were looking for exactly, it will feed data to your GP33 and Navpilot 300. I would not recommend having the SCX20 on the same radar plain. Recommendation would be to have it above the radar. If you can provide us some pictures of your boat, we might be able to help with recommending a good mounting location for the SCX20.