The engines I use are also the 31cc version. I have an "IDC" and a "Ryan" too. Have you seen the "Evra"? It is just a factory converted Ryobi 31cc with mounting lugs built into the crankcase. It is too bad that they are not still making the case. It would be well worth the cost of tooling up to sell to the folks who like the engine. It was distributed by Hobby Lobby. I found one at a swap meet with the original box and all of the paperwork. It has a notched pulley on the front to rope start it. I have seen them sell for over $100 on the net. It was sold as the " Evra 190".
I still wish someone out there knew how to read the numbers on the coils and tell them apart. I will try the coil off of the Ryan next to see if there is a difference.
Thanks again for your info.