not too sure what datsun 5 speeds have a model number starting with "F" you could try to get a 63a box as they are very strong and shouldn't give you any troubles.
You say you have a toyota box, is it a 5 speed celica box? if it is you can use the 3spd datsun Automatic bellhousing to couple the celica 5 speed to your A series engine as it is quite a common transplant, you would then need to modify your tailshaft to take the toyota splined drive input at the back of the box. I live in Australia and you don't see many 5 speeds in top condition pop up very often, although it probably doesn't help that I live in western Australia also known as the wait-a-while state!