If you go to this page on the HBR receiver website you will find a chart listing the experimentally measured bandwidths for the BC-453 IFTs, with the micarda rods in, with the rods out, and also some oscilloscope traces of the skirt:http://www.qsl.net/k5bcq/HK/HK.html#AFEW
(Depending on the size of your computer screen, you may have to scroll down a bit to get to the chart and the scope traces.)
There are readings both for a single IFT, and for a circuit of two IFTs. For a single IFT the result was a BW of 3.0 KHz at 6dB down. When a second IFT was added, the BW with the rods pulled out on both cans dropped to as low as 1.8 KHz at 6 dB down.
73 de Martin, KB1WSY