Hi ArmedZagi,
I'm a bit stumped here, looking at the setup you have I would think it would be OK with the 12-8 prop and gearing down 3:1 and only running a 7.2V pack. The Tower website does not give any real specs on that motor and I don't have a program like MotoCalc to crunch the numbers.
To use the Props that you linked to from Hobby Lobby, you would almost certainly have to buy the complete yoke/spinner deal to use Graupner or Aeronaut props (these are the "better" folders for gliders, I use both
)
One other thing I wanted to clarify on charging Nimh cells, they should not be left on a "trickle" as the lable states, but a "slow" charge is not a trickle.
A trickle charge is usually a rate of 1/50th of the battery capacity, in this case only 76 Ma, this is used to maintain the charge on Nicd batteries after they are fully charged, but will cause problems with if done "long term" on Nimh batteries.
A slow sharge, or overnight charge is done at C/10 or 1/10th the rating of the cells, in this case 380Ma for 14 to 16 Hrs, this is always prefered for charging when time is not a issue and for "forming" a new pack, this slow "overcharge" of the pack allows all the cells to equalize slowly and come up to full capacity, see if you can set your charger on slow charge and a rate as close to 380Ma as you can.
I wish I could be of more help on the motor issue, after the Holiday why not give Tower a call, their techs may be able to give you some more help on prop choices.
Good luck, and Happy New Year,
pete