The crash box has a large nut on the front of the turret for the gear lever, the synchro boxes don't.
Some synchro boxes had synchro on 3rd and top, some also on second. I'm not sure you can readily tell the difference without looking inside.
<edit> unless you've got a 3-speed box in there, in which case it's a crash box...
Some synchro boxes had synchro on 3rd and top, some also on second. I'm not sure you can readily tell the difference without looking inside.
<edit> unless you've got a 3-speed box in there, in which case it's a crash box...