ORIGINAL: coriolan
You can do the break-in on bench with an aircraft prop as load but since its a water cooled engine with no convection fins you'll need to provide water circulation. The ASP engines are ABC type and don't require a long break-in( a few bench runs should be enough to have everything fitting nicely). Some nitro (5/10%)makes idling better but not important,mixing a FAI blend (80%methanol-20% castor)would be fine too and at least you'd know exactly what is in your fuel!
I think I'll break in the engine without the propeller 8 X 6 because you can not find the firewell to taper.
I have a 42mm propeller, pitch 1.2, I do not know if I replace while waiting 40mm propeller, and pitch 1.4 (break-in the engine)
( I ordered a prop, 38 X 1, 4 and 40 X 1.4 )
I did the engine mount with damping as pics below.