Im putting my spark ignition gasoline converted OS 160FX (more powerful and lighter compared to a real 26CC gasser) into a 120 size pattern ship - world models spot on 120.
Dry AUW is under 4500gr. with 17x10 prop; generating 7+kg of thrust, it should move fine in uplines.

Also I got my other converted 160FX going into a Sebart Katana 120 (1870cm span), with 18x8 prop, it should also move and hover nicely with 8kg of thrust. AUW estimated 4300-4600gr.

For unlimited 3D, keep thrust:weight ratio between 2:1 - 1,5:1
For fun sport flight keep it around 1,4:1 - 1,2:1
For scale, floater planes, you can do 1:1 or 0,8:1

all ratios are MHO.