How to assemble 049 engine?

What kind and/or size of screwdriver are you using to try turning the screw in? You may be using either a screwdriver too big or too small for the screw head. Just another possibility. Or, as I believe was stated earlier, and if not, here it is now. Without the engine, screw the screws into the mount to cut the threads, remove them, then re-install with the engine.