I've flown my UCD 3D with a host of various motors:

ASP .91 2-stroke
Saito .91
Saito 1.00
YS 1.10
Enya 1.55

With the .91 2 stroke, full throttle thrust is adequate, but the throttling response is poor when using a heavy prop like APC 15x4W. On the other hand, APC 14x6 gives pretty good thrust too with better response. But this plane benefits from extra prop wash going over the tail. So you can try both of these props and see which one you like better.

Saito 91 is a little under powered

Saito 100 is about right, but I like a little more. Maybe Saito 100 w/ 30% heli fuel would be perfect

YS 110 is more power than it needs, but I now have floats on my UCD, so the 110 pulls the extra weight nicely. I do not feel 16x4W prop is a good match for this engine. I tried this prop, and it swings it at over 10k rpm. I felt using APC 16x6 @ 9900 rpm makes the plane perform much better.

1.55 4-stroke is just too heavy for this plane. The extra power you get does not justify the weight gain and nose-heaviness.