most planes have the down and side thrust built into the firewall so you can use a regular engine mount. Of all the kits I've built I can't remember a single one that didn't have the angle set this way. I have built some profiles that needed washers added to get the side thrust set correctly, I would imagine that you could set some small washers between the rear engine mount holes and the mount to get a few degrees of down thrust.

What plane are you using your mount on? ARF or Kit?