Proper size beam mount will suffice.
Standard servo is good.
Personally, I always use the " KISS " method. Being Polish, this is not very hard for me to do. Hahahaaaa
" Keep It Simple Stupid "
Hangar 9 has a nice mount. I have one myself, but have yet to install it in any of my models. It is already drilled and should fit a DLE-20 perfectly.
Read the following:
Enter the Hangar 9 Ultra Engine Mount. The Ultra Engine Mount can be used with a wide variety of engine sizes; from .58 2-strokes all the way up to big 1.50 four-strokes. With this mounting system, there is no drilling and tapping necessary. Twin, slotted-aluminum beams hold the engine in place, but allow adjustment of the fore/aft position of the engine simply by loosening the mounting bolts.