I continued on my quest to find affordable LNBs that allow easy modification for an external clock reference. The Goobay 67270 Universal Twin LNB also seems to be a good candidate. Under the same product number there appear to be 2 variants: One has a SMD crystal, the other has a through-hole crystal. Both can easily be replaced and a 2.2 uH / 18 pF series LC circuit connected to the first crystal pad will complete the mod. The needed drive level was about 1 Vpp.