The simplest way would be to just replace the 4dtv with the v-box. A diseqc switch can choose Ku or C-band cables. Might have issues on vertical polarity though so a powered switch or power inserter can be installed on each cable so the LNBs get 18v. Think there is a circuit you can build to control the polarity servo somewhere (other members might have this bookmarked) using high/low voltage signal from the receiver...
Second: If you can find an ASC1 it can do the skew on your Chaparral feed horn and a diseqc switch can control which input (C or Ku) to select for each satellite. You already have a V-box, don't think they do skew though so this unlikely to be an option, would actually be the simplest though...
Third option would be a bullseye type feed horn with four LNBs and a milti-switch to power the LNBs, that gives you C and Ku on the big dishwithout the need for the polarity servo.
Fourth: replace the feed horn and LNBs with an LNBF. Brian sells some good ones. Go with C-band only on the big dish and add a motorized Ku dish for Ku. The Ku dish would use USALS/Diseqc control so the cable from the receiver goes to the Ku motor, then split off using diseqc 1.0 or 1.1 switch to Ku LNBF and C-band LNBF.
I did this many years ago, never did the bullseye option was too pricy for me at the time... Currently using a spider's web of cabling, switches, and many dishes. I should make up a schematic some time...
