You should be shooting about 51-52 lbs. I think Big Jim bows are cut to center. Agreeing with Paul at Badger arrow, that would mean a 60-64 lb spine shaft for a 28" arrow and 125 gr point. I think you would be OK with a 160 gr point at this spine, too.
Ash is definitely at the top of the heap for tough arrow woods, but it is also quite heavy. Fir is pretty tough, carries good weight and is a great shooting arrow wood. POC is a fine arrow wood, but has a reputation for being less durable than most woods. Sitka Spruce is also a good, durable arrow wood, but pretty light in weight. My choice is fir.