You can make the receiver better. . . in fact quite nice. Do the 6Kc filter thing and use an external AF amplifier. The TX requires major dehnyellification. I don't think any one has done it yet. Pressed to perform I would locate the DBM and use an external AF chain and impedance matching/isolation to feed it. . . . this site might help you with the reference materials;
http://www.geocities.com/k3xf/ic706.html