Depending on the vertical C.G . , room aft for tank , ply doublers etc etc ,
Whittling the bearers down to 1/8 wide , aft of the firewall , isnt unusual . Even on front induction layouts .
With the ' crutch ' layed ON TOP of the sides & doublers , the cavity can be a full two inch width .
Used this on the HP 40 R.P.R. in the Folkerts , and will again in the GOON .
sent a picture in the P. M. . to you .