Choice of 515 in a 210 center cabinet

[Phil-G]

They'd give you more LF extension at the cost of a tad of midrange sweetness.

But, you're not going to do it without irreversible mods................ either cutting the woofer frames, or chiseling away at the insides of the cabinet until there's only about a 1/4 inch or less of plywood left between the woofer cavity and the outside world.

or buy that slightly scratched one the guy was selling on ebay.
Altec Lansing 515 16g LF Woofer Speaker Cut Side 15A | eBay