Number three is your best choice. Get one of the Dave Brown mounts of the correct size for your engine. Drill and tap the mount to fit the engine. The Dave Brown mounts can usually be removed from the plane with engine mounted if needed. They have center lines cast on the radial part of the mount to make alignment a snap.

I just finished my second ARF, a Phoenix Fun Star (crashed my four star 60 and needed something other than the trainer to fly and didn't have a kit far enough along). It had the type mount you are talking about. The kit calls for either a two stroke 40 or four stroke 52. The mount may fit the two stroke, but was about an inch short for the four stroke. A little work popping out the blind nuts and putting a donut with new blind nuts to fit the Dave Brown and I was in business. There are other mounts that would work, but the DB's are inexpensive and easy to drill and tap.

Don