Bjorn Andreasson was working on Convair jets with very thin wings when he designed the prototype. Maybe some of that came through in the design.
Before that he worked for
Skandinavisk Aero Industri A/S in Copenhagen, who built the KZ range of light aircraft. I've always wondered whether he got the inspiration for the Y-shaped central stick in the MFI-9/Bölkow Junior from the same control stick in the KZ-IIK, KZ-III and KZ-VII?
As for interior dimensions, the Bo 208
C variant should provide a few extra centimetres over the earlier versions.
Some years ago, a Czech company had plans for a Rotax 912 powered microlight variant of the Junior and displayed a prototype at the "AERO" exhibition in Friedrichshafen/Germany.
Allegedly, Björn Andreassons plans for the MFI-9 (the progenitor of the Junior) are still available if you want to build one yourself...