The 91 OS FS didn't fit. It's been a while but maybe I could have ground down the mount more?? The SK is a two stroke 91 and it fit, it was tight but it fit, but I got it in there. As I recall I got the mount in then built the cowl around the engine. I could remove the engine but not the mount? I don't recall but I think that's how I did it?
Blue Jay is still cutting and selling the Kaos in the 80 inch so if a 60 size isn't big enough for you then that is a kit option. I had my 60 size and the 80 inch for about 20 years and killed them both in the same year.
The one they called the 90 size is not cut by anyone I know of but I have seen the plans in MAN.
Another good choice is the Ultra Sport. Minn and I used to call it th grand son of Kaos! It has the same wing but most old design pattern planes do too.