Other than the attached weight on the externally balanced flexplate, what are the other differences. I need an internally balanced SFI approved flexplate but there is an externally balanced flexplate for sale about 3 miles from my house for $10. It is new in the box and the owner wants to get rid of it. Can I knock the weight off and save $200? Am i barking up the wrong tree?

 

While that can work, you will still have to confirm that the flexplate has a neutral balance. This can still be affordable, but if this is for your truck, you might not be within the SFI regulation any longer.
According to the standards for specialty/performance automotive and racing equipment the original part cant be modified or it loses its certification.
Maybe that is not such a big deal to some, but I am confident that your ride would only get the best parts with regards to saftey.
Is this a gray area? Perhaps, but this is just my take on this.
Will you idea work? Yup, I have knocked off several weights on other engines to make this work.

 

I went ahead and bought the one for $10 and a new one from Scat. It was only $58 for the SFI approved one.