I think part of the reason for little information or enthusiam is the
diodes tendancy for IMD on strong signals. This increases the
complexity of the circuit. You might check with the ARRL and see if any
information is available from past QEX articles. I am researching the
same thing for a HF preselector. I am going to experiment with solid
state relays. Just a suggestion. Try the Vishay site
as(http://www.vishay.com/solid-state-relays/). I have found little info
on varactor tuned pre-selectors