Enzian, Rheintochter R-I (and R-III), Hs-297 Schmetterling, C-2W Wasserfall (at least 12 subtypes W-1 - W12) and Feuerlilie (F-25 and F-55) to name the most important SAM projects. The X-4 anti bomber guided AA wasn´t a good solution at all. The R4M is quite more interesting, it could be used against ground forces as well.
The MB-3 with six 20 mm mounted in mid wing position are definetly too much for such a light airframe. I expect that the recoilforces would harm the wing badly, not to speak of directional stability while firing.
Hadn´t the VVS a 23 mm gun? what are the performances for it?