Nice shooting. That is super with open sights and the first time out. The 535's from No Excuses shoot great for me with 75 grains of Goex 3f.
As for the dowel. Myself I would do it. I consider it like a cheap insurance policy because it would be so hard to get a replacement stock but like Cayugad says you might shoot that gun the way it is for your lifetime with no problems to the stock. You really got a great bargain on that rifle. I think all the .540's had the Wilson barrel with 12 lands and grooves. Congrats!
Art