I own a VFC HK416 and worked on my friend's VFC SCAR-L, both are excellent externally.
I think the SCAR is a bit tough to work with, especially if you are doing this for the first time. After working on numerous guns, I still think the SCAR is not as straight forward as your regular M4 variants. But if you're up to the challenge, it can be a good learning experience.
And, mosfet'ing a SCAR is possible. Not pretty, but possible.

This is a homemade 3034 mosfet.