Dick is pretty much on the mark as usual.

if you're just stuck on a DA 50, it can be done, but it's going to require more work from you if you want it to be "legal" as a pattern airplane.

Your only limiting factors for legality within the rules are:

Less than 78.74" (2 meters) total length or wing span
Less than 11 lbs (or 5kg) total weight without fuel (or gas)
Less than 96db (but I haven't looked lately, they did tinker with the sound rule)

At the risk of "pushing product", let me say that a local guy named Dan Holzworth has now built 2 Black Magics around 10 lbs 6-8 ozs with an evolution gas engine (same as mvvs). A ZDZ 40 F3A would be ideal I think. It might be a couple of ounces heavier with that set up, but it is fairly easy to do without having to pull your hair out, and it would CERTAINLY have enough power. There's nothing "magic" about the Black Magic series of planes, on the contrary, they are very simple and that's the key. if you wanted to have a more traditional wood/foam/glass type of airframe, then this one does work very well for what you're looking for. It is not an ARF and you have to build it. But the VF3 is an EXTREMELY capable competition plane and it's all laser cut, self aligning and very simple.

If you wanted a composite plane, I know some out west have had some good success with the Abbra and the zdz 40, but it can be difficult to get one at times. Others may or may not hold up to the harsh nature of a gas engine.

if you try an ARF, then well, good luck, it's a crap shoot. if you find one that'll make weight it more than likely may have problems holding up under that engine. That being said look around and maybe take a shot at it.

From what you describe, you are dead set on a DA 50. if that's truly the case, then good luck, and if you do manage to get it legal, please post the info here because we all want to know about it! Complete with weights, pics and all the juicy details!

-Mike