...I am currently using four 9 MHz crystals in the filters...
4 crystals makes a good casual filter, but not one with sharp skirts. Most commercial
rigs (at least before DSP) use at least 8 poles to get the desired selectivity. My old
Argonaut 505 had a 4-pole crystal filter and got great audio reports, but it was about
2.7 kHz wide and suffered in a crowded band. Since you have separate filters for TX
and RX you can optimize them for different characteristics if you want, or build several
filters to switch among. My Argosy came stock with a similar 4-pole filter and I quickly
decided that the optional 8-pole filter was a good investment.