cayugad

Yes of course you can use pyrodex in it. As to the barrel twist I would guess it to be 1-66 or 1-48 you will have to check it to be certain. What's the barrel length on that rifle. Usually if they have a real long barrel they are more incline to be 1-66 twist which is for shooting roundball. The full stock Kentucky style rifles were usually (but not always) 1-66. As they became more in line with other rifles, some of them began showing up with 1-48 twists.

I'd start with a .490 ball and patch combination and keep the powder charges under 100 grains of 2f and you should be fine. With about 80-90 grains of powder if it is a 1-66 twist the rifle will probably tune in. Also it should shoot good with about 40-50 grains for plinking rounds...

To find the rate of twist, put a cleaning jag on the end of your ramrod. Put a tight patch on the jag and push that to the bottom of the barrel. Take white out, and mark the ramrod and the end of the muzzle. Now pull the jag up slowly, letting the ramrod turn at will with the rifling. When it makes 1/4 of a turn measure that distance from the dot to the top of the muzzle. Now you can figure the twist. A rifle with a 1-66 twist, the dot on the ramrod would make a 1/4 turn in approximately 16.5 inches. If the rifle has a 1-48 twist it would make that quarter turn in approximately 12 inches of space between the dot and the rifle. Now granted this is not 100% positive, instead of 1-66 it might be 1-60 but it will give you a working approximation...

Good luck with the rifle. There are a lot of Spanish gun makers that sent rifles through one company or another to the United States for sale...