We've been able to reverse tractor beams for a long time now. Also, 300 or -300 is the default/what valve uses.
As for the map crashing. Are you sure it's not something triggering the crash? There could be a trigger misfiring, or anything really.
Please add this to the OP:
ALL 105 ORIGINAL PORTAL 2 MAPS DECOMPILED, WITH STATIC PROPS AND FIXED ROTATIONS ON INSTANCES: http://dl.dropbox.com/u/813382/VHT/Original Maps.7z