Thanks Jim, knew I could count on you.
I'm going to call Butternut on Monday and order the two sections of aluminum. I could use the top section of the "parts" HF6 I have, but it would make the antenna a foot shorter... probably not enough to make a difference, electrically. Still, the cost of tubing shouldn't be that much (DX Engineering sells 6 foot lengths for under $7 each, so that's the backup if Butternut wants too much), and I'd rather restore it correctly.