Dan,
If you don't have the Porsche manuals, the top photo shows the adjustment between the 1st/2nd and 3rd/4th shift rods, roughly 2mm-3mm. As John says, make sure the forks center the sleeves between synchros. Shift one rod into gear, then make sure the other is locked out, so you'll know the rear plunger is in position. Put the rods in neutral when installing the midcase. Make sure the nuts holding the guide fork to the access plate, bottom photo, are secure.
