Lucas,
Your fan should be a 12'' blade, mine is a 12'' overall (305mm diam). But I think yours if fine for the side of the radiator you want to fit it on.
I fitted mine on the other side because I had to turned the radiator around to have the lower water inlet on the left side, and the high one on the right side : it is much better for my engine set up. But that way, I needed to fit the fan on the radiator's side where the core's side plates are offset and not flush. So I had to chose smaller diameter to fit the fan in between those two offset side plates.
If you fit your fan on the side where the side plates and brackets are flush with the core, the diameter you chose is good : it covers a bigger surface than mine.
To fit your fan, remember one very important thing : the fan has to be flush with the core face, it has to be perfectly against the core, to touch it. Otherwise most of the airflow it will suck will not come from trough the radiator, but from the sides.
Also, as already mention on this forum, a puller fan is more efficient than a blower fan and should always be preferred. Blower fan should be installed only if there not enough room to fit a puller between the radiator and the engine.
I didn't want to fit mine trough the core with the lock ties either, but it looks to be a very popular way of fitting fans, used a lot on racing cars. I had no other choice, so I did it this way, and finally, I'm fine with it. Just be very careful when you enlarge the holes in the fins not to damage the tubes.
Good luck
