I can certainly appreciate the importance of saving money where possible, and I can look into this for you if you are able to provide the part numbers of the units (including all parts) being used, and the N-number of the donor and new aircraft, then we can see what additional equipment is required. I get this call daily, in fact about 5 different versions of it yesterday...
The first issue is that a 60-2 is not a 60-2, it is a collection of parts specific for one make/model/variation of aircraft. Most all of the major component part numbers and hardware kits are different for different aircraft models, it has nothing to do with the parts being new or used, it has to do with the fact they may not be the correct part numbers for your specific aircraft model. Each different model aircraft has different flight characteristics so the computer and servos require settings and gains specific to model of aircraft they are designed to go in, autopilot computers/controllers and servos are not “standard,” they vary by airframe. For example, if the Autopilot System was coming out of 340A and going into a 340A then it MAY be possible with typically just needing a re-install kit. Going from one model aircraft to another though this is not typically the case. In either case typically a used AP system will NOT include a complete hardware kit or serviceable cables which is why you would need the re-install kit (hardware kit, cables, and the install documentation paperwork). The re-install kit is available for 50% of the list price of a new system.
The difference in part numbers is reflective of the differences in gains and settings on these components. The computer and servos will each need to be returned to the factory to be reconfigured for your aircraft make/model and have the part numbers changed to reflect those required by the STC if they are not the correct part number. The price of sending back each servo and controller to be reconfigured for your aircraft, and purchasing the re-install kit for your aircraft will likely be near the cost of a new system, it would likely make more financial sense to purchase a complete system
You should also find a dealer who is willing to install the system as some dealers may not want to perform this service, and we are only authorized to sell the necessary components and paperwork to an S-TEC dealer who will be doing the install. You can find a list of dealers in your area on this link:
https://genesys-aerosystems.com/dealer-locator
I have an S-Tec 60, and I'm looking at a 60-2 (with altitude hold). The advantage of that system, for me, is that half of it is already installed. If I were starting from scratch, I'd be looking at some of the new digital systems on the market today.
The 60 series came as a 60-2 (dual axis system), 60 PSS (single axis pitch control), or the uncommon and not longer available 60-1 (single axis roll control). We do have an upgrade path from the 60 PSS to the 60-2 (Mid Kit Sixty 1, i know the name can lead to some confusion) which is a list price of $9,989 and includes all the necessary components/hardware (programmer, roll servo, hardware/mounting kit, cables, roll flight guidance computer, turn coordinator). Alternatively, we have an upgrade path from the 20, 40, 60-1, or 60 PSS to the 3100 fully digital attitude based system for the 182 series. This is $12,495 if you already have an S-TEC electric trim installed or $13,995 if you do not. This would give you all the benefits of a new digital system a 2 year warranty on the new equipment AND a fresh 1 year warranty on your existing servo(s) regardless of age.
If you have any questions or if i can be of any assistance please let me know! Thank you and have a great day!