So, to be a bit more specific, the CVA, Traditions and other Spanish percussion guns typically used a 6 x 1mm nipple.
On the other hand, the other European percussion guns (Lyman, Investarms, etc. used a 6 x .75 nipple.
Then to confuse matters, some of the Pedersoli guns used 1/4 x 28.
I agree with Fyrestyk, it is probably 6 x 1. And of course, go with stainless steel instead of blued steel.
I think your charge of 35 grains, .490 ball should work fine, but maybe you could also try 25 grains as well. Actually, I would personally start at about 20 grains and work my way up by 5 grain increments to the tightest group. I would also try FFg vs Fffg. And maybe some .495 balls. Then you can try different patch thicknesses. It's all fun. Of course, shoot from a rest with load development.
Do groups of three shots per each variance. As long as you are hitting on the paper, wait until you have the group size you want, then adjust the sights.
Let us know how it all works out for you.
John (Bigsmoke)