ok i see the pics now
those mws blades are different to the ones i had ......mine were the smaller " game of thrones " variety , those look much better
so you have roughly a 2m diameter prop . sticking to the stall issue you mighnt have to go much bigger to improve the situation a bit . a 3 blade 2.2m maybe ...
i,m not sure i,d like to push more than 500w out of the alt , theres plenty of posts on the net of burned out coils on alts slightly on the edge . i,m not positive about that but you dont want to push for the high figures ...more consistant lower power levels would be easier on the alt and let it furl out early
the ebay blades ...a 2.6 m prop then , now seeing the alt i think their to big and if there good quality and run as fast as they should they might burn out the alt. plus......... there fibre glass and might ( probabely will ) be pretty heavy , possiblely 3 times heavier that a basic carved cedar wood prop of the same size , thats going to be hard on the linear bearings in the alt ...not good......and your going to have to customize the hub mount to suit the alt .....
your really in ideal terrority for carving a 2.2m 3 blade prop from something like cedar or any reasonably clear wood , if it doesent work out its really only cost you your time and its nice to see your own work up there.....
from the very little experiance i have and reading others posts about matching the prop to the load its a very tricky business getting it right first time ( i never could ) especially of ebay .....i bought 3 sets online and none of them worked out ...almost.......but not ....its hard to tell with the ebay postings what quality you actually get.
i,m still wondering about some short 6mm plate extensions for the prop blades at the hub ...its not ideal but a cheap experiment , hacksaw and drill terrority .....if it doesent work thats ok
when the prop goes in to stall what power is the alt roughly putting out Turbomiles ? .....your mast looks pretty high
sorry not really much help
ps....if you are tempted to make a wood prop heres a link to a nice 2.3m design http://www.scoraigwind.com/selfblade/index.htm
its a powerfull prop so furling would need to be adjusted