Drill and tap the manifold, you can use a pipe plug on the current hole. Easy stuff.
And you are correct it may not tell you more but why risk it when all it takes is drilling and tapping to eliminate the possibility? I suspect just moving it and tapping the manifold will help, that threaded bung you welded on looks to be at least 1/2", combine that with the length of the compression fitting and your way out there.