Get the engine hot and then turn it off. Loosen up all the engine mounting bolts; not sloppy loose but loose enough for a little movement. Start the engine and torque each mounting bolt while the engine is running. This helps to get rid of any internal stress in the frame/engine mounting.
Uh, why did you buy an Enfield?
EWSDI assume you have checked the head steady to see if it is cracked or its fasteners are loose?The other engine mount bolts have been known to be loose or to fail.If either of these areas have cracked or loose parts the engine vibration will be very noticeable.