4-pot adaptors from Russell (enim57) with instructions, with Nissin calipers.
Fits early Concours 86-93(?), the ones with single-piston calipers.
Fits stock-size rotors.
Never installed, so unsure about caliper seals. Come with used pads.
Also s/s lines, came with calipers, look too short for a C-10 but not sure.
I have $200 in this, will sell for $120, shipping to US 48 included.

Reduced to $100.

Now on ebay. Item 261551868582.

Thanks to Russell (enim57) for use of pic of installed calipers.

I already have this this but for someone out there with an early model, this is a very good deal.

GeeBeav, you didn't mention which diameter rotors these work with?

I built a similar set up, that I use on my Connie. (03)
I built mine to work with the stock rotors, as I didn't want to change rotors too.
With the 4 Pot calipers the stopping power is better than stock.
If these work with 120 mm rotors, they would be even better.

Ride safe, Ted

Would these calipers work on an newer model with different adapters and bigger discs?

Warsul, the Calipers would fit, but the adapters would not fit your Later Model C-10'.

You can buy Nissin or Tokico calipers on Ebay/etc in this design, but it's difficult to find them for $100, and difficult to know which calipers to buy.
So, this is not a bad deal for you.
BUT,,, it is a great deal for someone with an earlier C-10.

Ride safe, Ted

GeeBeav, you didn't mention which diameter rotors these work with?

Stock size rotors, as stated in the OP.

Thanks for all the comments.