Might not be to too unfeasible to heat up the tube really good with a heat gun or something and slightly melt the tube to get enough clearance. Don't know though, might make matters worse if it doesn't work out that way. I sort of shopped for price wise, but the big thing was just the size in general. Here is what I ended up with:
Spacer might work too, just have to estimate as best as possible (pad up a little for speak flex) for how much clearance before wasting any time. Speaker might get louder in the dash (speaker diffraction). Also verify that +/- are hooked up the same on each side. If one is backwards, they will be louder left/right side, but quieter centered.
If it doesn't work out, don't get discouraged from doing other things later on. As you run into this stuff, you will tend to get better and better at making stuff work. Worst scenario is you'll have to sell what you have and find something else that will fit.
Pete