Will the crowns be for Chelem, Toviyah...?
Rashi: The verse should be re-arranged. The crowns will be in Heichal Hashem, for a good remembrance for Chelem and Toviyah who volunteered the silver and gold. Those crowns were hung high in the Heichal, like it says in Midos (refer to 6:14:1:1). Chelem is Cheldai (10). Radak - he had two names. Chen is Yoshiyah (10).
Radak #1: Each crown will be a remembrance for them in Heichal Hashem, like it says "l'Zikaron Lifnei Hashem" (Shemos 28:29). I.e. their gift will go in front of Hashem to benefit them in this world and in the world to come.
Radak #2: Coming generations will remember them, for their names are engraved on the crowns.
Malbim: Yes, now they are for them, and not for the king or Kohen Gadol.
Where in the Heichal are they?
Rashi and Radak citing Midos (3:8): Gold chains were fixed in the ceiling of the Heichal. Young Kohanim ascend on them and see the crowns in the windows, like our verse says. Radak - they were put there after Zerubavel and Yehoshua wore them. Malbim - this is so Yisrael will recall what they must do. If they will repent fully, it will be the time of Ge'ulah, and the king and Kohen Gadol will wear the crowns!
