Your woodworking looks excellent. It is said that the mark of a good carpenter is how he finishes the inside of a closet. Even though those internal braces will be inside the speaker cabs, they are nice work.
As long as you're getting the right part, go for the best price. I think the Meniscus Audio kit may have a better price than all the parts if purchased separately.
That one is too large, 4" diameter. The design calls for a 3" diameter port (see post #2 in this thread).
- If you get a non-flared tube, it should be 2¾" long.
- If flared on the outer end, make it 3¼" long.
- If flared on both ends make it 3¾" long.
They all will get the job done.