I was down geting a 60 of GP the other day and I noticed that Andrew had some stuff from P.O.R, on the shelf it think it was called "satin subframe black", the tin said it was to match US engine bays, subframes and suspension components.
So if you not keen on 2k maybe give that a try. Septone also make a Subframe black acrylic, which is kind of a satin, I think it would be ok. Make sure you don't get Septone chassis black it's like brown tar.
The GMH black you buy is watery crap, useless execpt for guide coat, and GMH black shouldn't be black anyway from the factory they used really dark grey.