Might still try it at some point. If I do I'll make sure to confirm it either way.

I don't think you can. It looks like the aircraft spawn points definition of the aviation club is defined using a different mechanism then a usual spawn point object.

I wonder if this invsicube can be fiddled with using the Building Spawn Points 1.2.3 Mod to find where the spawn point is outside the 8x8 area and then move it to be in line with a custom runway. Then you just need to set the aircraft you want to use that runway. (Instead of building the runway to where the spawn point is like your description says.)

I don;t get what you mean, if you want the building you can either use the vanilla one or you place whatever building you want on it. It's called modular because it is designed for you to customize it in whatever things you want to put on it

Can you make this with the building?

Nice asset :) I used it to create a small grass airstrip.

I have no experience in really looking into directly modify the predefined object in game. I don't know what is the actual in game system of this, but I suspect (from my programming experience) that it should involve some large object definition change, or even define a new one inside to work. That is not really an easy task., a totally different level of work compared to asset creation .

Just wondering about going the next level, like adapting the aviation club and its runway to be used with Airport Roads.

Good stuff Tiger!