I suggest flying the plane 1st, then decide if the engine needs any right/down thrust.

MOST planes only need the right thrust to counteract the prop torque on takeoff (use the rudder to counteract the torque )

If it does need right thrust, I use washers between the motor mount and the firewall and for down thrust between the rear bolts on the engine and the motor mount. A variety of thicknesses can be found in the FASTENER section of most hardware stores (Ace, True Value, etc. )