Shipto,
I'd be inclined to fill from the bottom, ie. a sprue on the split line so that the bottom of of the sprue is below the bottom of the mold chamber, catching anything heavy, I'd put a riser above the part to compensate for any shrinkage. If you're going to make several molds, I don't see the advantage of putting them in the furnace! It's hard to evaluate your proble without dimensions!
Regards, Matthew