The chipmunk is good value and a great airplane but I am spoiled now by modern CAD based designed. The spar slots need trimmed and shimmed to get good alignment.
The wood density varied to very hard to only slightly hard. The very hard wood was right on the ribs that hold the gear blocks so that is where you would use real hard wood. bottom side Trailing edge sheeting held on with weights
Now the real advantage of the jig, I can flip it over and keep everything in place