The barrel should measure at 24". The original sight is I believe a standard bead on blade. One thing I've found that I dislike about the CVA adjustible rear sight is that when adjusted all the way down (the position that I always start with and often find is where I want it for 50-75 yard shooting) the elevation screw head will obsure the notch in the rear sight. If I were you I would consider a slightly taller front sight that could be filed after your most accurate load is found with the rear sight notch unobscured.
My Frontier .50 likes .490 round ball with a pillow tick patch; I've used 3f black powder (because I have it) from 45 grains upto 65 grains and gotten good centered groups. I did try lighter loads just to see, but, they opened up a bit.
If you just want to replace the original front sight I think that Deer Creek probably has it.