Take it to a gunsmith. There's an awful lot that can go wrong on this job. If you do it yourself, apply some penetrant to the bushing threads 24 hours before attempting to remove them - not WD-40. SiliKroil or PB Blaster, for example. Have a bushing tool (see Brownell's) ready. Look inside the frame to see if the bushing has been 'staked' to the frame to prevent it from turning when loosening the grip screw. If it has, take it to a gunsmith or cut the bushings down as already suggested. If not, go ahead and unscrew them using the bushing tool. Don't play around with them, hit them with all your torque right off the bat. If you have a stuck one and try to use a regular screwdriver on it, you'll probably strip out the driver slots in the bushing. All you can do then is to put a grip screw in the bushing so it won't collapse, and start it turning with a needle-nose vise grip. Like already stated, use LocTite when installing the new bushings, and be extremely careful not to cross-thread them. These bushings are one of the weak points on a 1911. If you strip the threads in the frame, a gunsmith may be able to restore them or oversize them for some repair bushings. They may have to be brazed to the frame, requiring refinishing.