1400 ish? Wheelweights with a little tin for good fillout will be hard to beat. After a week or so they will test around Bhn 11 or 12. One advantage of going to the softer side, it will give you a better chance, a wider window if you will, to obturate if your throat seal is not perfect. Lyman #2 is around 15, so the throat must seal, going down to 10-12 the powder charge may make it seal even if it isn't a perfect fit. Food for thought. Powder coating may be the easy button. Not my area.
I notice Accurate molds has 35-180C pattern for the .35-.351 SL's. I once considered the .351 for a Martini Cadet conversion, but have more ideas than money.
