Stainless 18-8 bolts yield a typical minimum of 65000 PSI, about 10000 PSI more than a grade 2 steel bolt.
https://www.boltdepot.com/fastener-information/Materials-and-Grades/Bolt-Grade-Chart.aspx

At a suggested torque of 66 in-lbs (~5.5 ft-lbs) the clamping force of a 1/4"-20 grade 2 bolt is 1320 lb.
https://spaenaur.com/pdf/sectionD/D48.pdf

I'm not engineery enough to interpret the Cousa test data to know if it will crush under 1320 lb of clamping force. However it does appear some balsa grades may be more resistant. https://www.corelitecomposites.com/...heets/BALSASUD%20Core%20Data%20Sheet.pdf

me thinks g10 or plywood anywhere there is a compressive load would be a good idea. G10 may be better in case water ingress is possible-- which it *always* is, right?