As stated the shifting drum has to be position between 3rd and 4th, but it might be between 4th and 5th. This needs to be confirmed. It is when the drum is in this position the fork shaft can be pulled out and the forks do not fall into the transmission. With the drum in position pull out the shaft, then push outer shifting fork back out of the way. Then I would install a long screw driver to keep the other two forks from falling while pulling out gear. With this done, ensure middle an inner forks are sitting properly and remove screw driver. At this point move second gear shifting fork back and out. It like cracking a safe.
Installing the new gear and shifting fork, if the fork was burnt/ discolored or scored, we be back racing on the street with speed shifting from 1st to second without problems. Also sometimes we would grind/file a notch in the neutral plate (Outer plate on the drum that has a notch for neutral) to supply a little extra force to keep second gear from popping out.
