Yes, the Orby dish uses a linear lnbf and the dish is similar in size to a DirecTV Slimline. There are several threads here about modding a Slimline with a linear lnbf for FTA use. Should be easier with the Orby dish as you can use the original lnbf so just point and scan. Keep in mind with a dish that size there will be limits as to what you will be able to scan in. 97W would be a good start, then see what else you can get. If you give it a try please post your results back here.
If you mod the Slimlines take really careful measurements as to where the center of the original lnbf is located and the angle it faces the dish. It is critical that the replacement linear lnbf be located properly in order to get a useful signal.
If you would like to keep the Orby dish intact (good idea) you can pick up a quality lnbf for experimentation on the Slimlines here:
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Use this LNB Bracket to add a LNB to any Directv dish, Dishnetwork Dish, ORBY Dish, Super Dish, and 33", 36", or 39" FTA Dishes. 30 mm & 40 mm LNB holder to fit just about any Ku LNB. Fits Standard/Universal FTA LNBs, most Dishnetwork and Directv.
Features a 30 mm and a 40 mm circular LNB holder which will fit just about any Ku LNB such as all Standard/Universal FTA LNBs, Dishnetwork and Directv LNB's. Use this LNB Bracket to add a LNB to any 18" DTV dish, Dishnetwork Dish, Super Dish, and 33", 36", or 39" FTA Dishes.
A quick video from Youtube to give you the idea on how/where to mount a linear lnbf on a Slimline. It's not detail rich but will give you the basic idea of what you need to do.