This is something I was unaware of, all my small frame pioneers run a .325 - they are some of my favourite saws. Plenty of torque, I use an 18" bar on most but have a few 14s and 16s.Many of the small cc Pioneer saws came equipped with 3/8" chains, the powerheads were reed valve induction and had more torque than piston ported saws make, they could pull the bigger cutters really well.
I may look at putting a 3/8 drive on a couple of them in the near future now that I know this