It looks as though you want to jump up to something like 16ft to get twice the power in the same wind speed.
2 x1 x1 magnets will do it well enough. To use 2 x 1 x 3/4 I think you are pushing things if you insist on running in stall mode. If you are prepared to increase cut in speed and loose a few watts on virtually windless days then you may do it with the 3/4 magnets.
To use 3/4 magnets I would be looking at increasing disc size and using 20 magnets ( not sure if disc size is set in stone).
I can't easily model the 2" round magnets and I have never had any experience of using them. I suspect that replacing rectangular ones with those 2 " diameter really needs bigger discs, most of the designs using them seem to have them crowded to close together so disc size might be an issue again. Keeping the same disc size I don't think the 2" diameter ones will do it comfortably and if you go up to 20 the disc size is certainly too small.
You could look at bigger rectangular blocks but I can't do much without knowing what you might have in mind.
Simplest option looks to be 2 x 1 x 1 with coils about 1 1/8" thick. for similar cut in speed increase coil turns to 1.3 times the present.
I see a very significant issue with wire size for a 24v machine. You will be needing the equivalent of 4 #16 in hand. The line loss is also going to be a big issue if it is any length. Unless you can keep the line loss down it is likely to get away from stall and you will have a different beast on your hands and you may get considerably more out but stator heating may become an issue unless you can control the furl.
For that sort of rating at 24v I wound my machine in 2 sections and brought 6 leads down to the rectifiers at the base of the tower, easier to wind but I was using a different construction and already had 3 wires in hand for each section.
Flux