It's not a big deal,i 'm assuming the 5 speed 60 series box has the same fork arrangement as a normal 1200 box.
You need to set it up and mark the area to be caressed,get the box out and take to it with a big hammer to get clearance.Alternately you can cut a section of the tunnel out and alloy box it over,i've used both systems without too much drama.
We had to do this also when fitting the Celica box.