The 'Juniors' used in Biafra, as far as I recall, were much modified with strengthened airframe, high mounted tailplane, more powerful engine, and underwing hardpoints for weaponry. I think they were designated MFI-15 rather than MFI-9.
The Juniors used in Biafra were more or less standard Swedish built versions. The aircraft was for sure developed as described, but that was later on. A guy I know built a very nice (and fairly accurate) replica Biafra Baby in the US, starting with a Bölkow built Junior airframe, but also installed an IO-240 for more performance than the originals. He sold it a while ago and it's flying. Surf around a bit on the net and you'll find photos.
Edit - EDMJ, we posted at the same time... Sorry for that!