Just my opinion, but why bother? If you are making a SBR out of an original HK receiver it would be Very expensive. As I recall an AOW needs to be made from a virgin receiver or a receiver that was originally a pistol. If the receiver came originally with a stock, it can only be made into a SBR. Since only a SP89 was originally a pistol, the conversion to an AOW would be very expensive if at all possible.
I have a Sear in a SEF pack that is married to a converted 94. The 94 has been remarked to "MP-5" with a threaded three lug factory barrel. It is a very smooth subgun. That's why I bought it. The Colt 9mm system has been problematic for me. Someday I'll SBR the host to have other options with the sear. I've tried a 53. It was fun, but didn't seem any smoother than an AR with the same length of barrel. Even buying a Vector host gun would be around $1,500 with mags and accessories. Of course you being a dealer, you could more than likely do a little better than that, but what is your time worth? It seems to me the HK system seems to be more suited to an HK smith than to a "do it yourself" type.
Yes HK has a coolness factor. If I were you I would actually try one before I spent a bunch of money to build one. Once you have actually tried one you'll have a better idea if it would be worth the money to you. Good luck with your project.
Scott