You can get a rotary drive from RayMarine. There are two sizes. Can't remember which I used but I'll see if I can find my installation manual receipts. If you use a rotary drive, you'll have to spec the sprockets correctly and probably procure those from somebody other than Raymarine. I'll see if I can find my parts list. You'll also need to purchase chain to go from the sprocket on the rotary drive to the sprocket on the end of the wheel shaft extension. See Rich' Stidger's 40.5 Mods post for pictures.
I think the advantage of installation ease far outway the disadvantage. Since it uses the wheel and associated chain/wire drive to move the rudder the disadvantage is that if your steerin fails, like a jamed or broken wire you lose your autopilot. The linear drive moves the radial drive directly so it may work even if the regular steering system fails. However, unless you are planning some serious ocean crossings I don't think that is too much of a big deal.
Where in Maryland are you located?
I think the advantage of installation ease far outway the disadvantage. Since it uses the wheel and associated chain/wire drive to move the rudder the disadvantage is that if your steerin fails, like a jamed or broken wire you lose your autopilot. The linear drive moves the radial drive directly so it may work even if the regular steering system fails. However, unless you are planning some serious ocean crossings I don't think that is too much of a big deal.
Where in Maryland are you located?