Re: Autopilot replacement recommendations
I went down the same path - looking for a Simrad wheeldrive. They used to make them, and older units can be found on ebay, etc. I emailed Simrad when I was still shopping, and they told me they have no current plans to bring back a wheeldrive system.
I don't know how well the NSS would integrate w/ the raymarine autopilot control box. I believe the NSS documentation stated that autopilot control would only work w/ a Simrad autopilot. If you already have the NSS though, and you're into that type of work, it might be worth spending some time spent experimenting.
Due to the popularity of the NSS, I didn't take a big hit when I sold it (on ebay). Maybe $350 or so less than what I paid, including ebay fees, IIRC.