Interesting concept, I personally would blend the catamaran hulls into the saucer but its nice.

Thanks mate. If it were 100% my design, then I would have probably done so as well, but then again it has a strong retro-feel with them as is...either way, should I design a later era vessel or even just re-explore the configuration for this era, I may
For some reason, I've always had a soft spot for that design, even if it did seem a little unrealistic (what with having two separate hulls only connected by a pair of booms).
I don't think I really need to say how good you're rendition on the configuration is. I should probably think about using markers to spruce up my sketches like what you have done here one of these days, since I've already been told once that they could really use them.
It seems that Armstrong is a rather common starship name in the Trek universe, used rather quite a bit by both canon and fanon alike, though given the lack of a registry number, I'm guessing that for the time being, this is only for fun without serious thought being given for actual design development, so this isn't really a problem right now.
I believe that Jefferies original intent of the configuration was to have those structures actually be just engines. The how to get to the secondary hull (if that was what it was supposed to be)that the engines are attached to, is anyone's guess. Anyway, I too loved the shape of it, and was why I wanted to take the reigns and develop her some more to honour a Great man.
Go for it with using markers mate, I have always worked in inks(it was what I started drawing with)...but its very fun. Nothing like doing things old school
As for the name, I am honouring the passing of a great aeronautical and aero-space hero...not keeping up with the Jones' sort of speak. This is, as stated above my way of appreciating Armstrong's accomplishments.
Well, that sketch does have a pretty dynamic angle. At least I think so.
And I can understand not worrying about little details such as registry or whether or not the name might already be used for that era. I usually start out a design to have fun and sketch everything out, and plan out the name and registries while finalizing everything.
Usually, when I think of old school, I think of pencils (and an eraser). Hehehe

I'll probably pick up a set if/when I go to an art store again.
It didn't even occur to me to mention that I knew that you were naming it after Neil Armstrong. I was already aware of the former lunar astronaut's passing.
JES has a thing about class names not being reused. Even among fan designs.
Especially among fan designs, since I see fan designs as a way to add to the Trek universe. But if a design contradicts anything else in any way too much, it can make it difficult to "work it in" into the fabric of the Trek universe.
Sometimes, I admit, it can be extremely difficult to not make some sort of contradictions, even with the effort to avoid them, but being aware is half the battle, which is why I sometimes mention potential contradictions that I spot.
In this case, it is fortunate that the canon (or semi-canon, depending on your point of view) U.S.S. Armstrong (NCC-1769) from the last film is supposed to exist in another timeline, so even though she would contradict another fanon vessel, at least she doesn't contradict anything canon.
In fact, seeing as how the Farragut in the alternate timeline isn't a Constitution class, I see no reason why the Armstrong in the prime timeline couldn't be another class as well. This Armstrong could very well be the same vessel for all intents and purposes, with the same registry. If all else fails, I know of no vessels that carry the full name (Neil Armstrong), which I think Starfleet might do if they are having a hard time coming up with new names. This all really only matters however if the design is to be taken further.