Dan,
Regardless of action type, you will be happiest with a shotgun butt, pistol grip stock and set (preferably double set) triggers. The Winchester Highwall was the best rifle of the period by a great margin. Lightestest action, fast lock time, strongest, best ability to seat stubborn cartridge, best ability to extract a stubborn cartridge. If you load quality ammo with black powder or equivelent pressure smokeless loads, then only issues 1 & 2 matter.
Lock time is only really an issue in offhand shooting but many good offhand scores can be shot with Sharps 1874 of Rolling Blocks if you do your part, in spite of thier slow lock time.
Action weight means you can put a heavier barrel on a Highwall than others and still stay under any weight limits, but again, many win BPCR silhouette matches with legal weight Sharps or Rollers.
Stay away from trap doors and others that can't be cleaned from the breach.
The rifles seen most in serious silhouette competition are Sharps '74, Highwalls, Rolling Blocks, and Stevens 44-1/2.
For what you want to do 45-70 is better than 45-90 in a number of ways. It's a better ballistic balance with less recoil for matches up to 600 yds and components and ammo are way easier to come by.
Pedersoli barrels are great, they compete with the best semi custom guns from Shiloh, C Sharps etc.
Pedersoli currently makes Sharps and Rollers, but is just starting to plan for it's production of a highwall. Uberti makes highwalls, but I haven't seen them advertize one with the right features as I outlined at the beginning of this post. C. Sharps, Meacham, and Ballard make excellent, though expensive, highwalls. Actually the C. Sharps is not priced too high, though more than Uberti.
I started with a C. Sharps highwall. It's the easiest gun to shoot well that you can imagine. However, I just couldn't see going through life without a Sharps, so I bought a Pedersoli Sharps in spite of any design limitations the Sharps has. I'm sure that sooner or later I'll have to have a Rolling Block too.
For serious silhouette competition the only front sight to consider is the one Steve Baldwin makes in Oklahoma City. If you don't have a spirit level beyond 200 yards you are seriously handicaped. Any other spirit level front sight will sooner or later end up reflecting a blinding beam of sunlight directly into your eyes as you are about to shoot, as I found out the hard way at a match in Arcadia, Oklahoma a few years back.
For combination hunting and less formal/shorter range target shooting a replica of a Beach combination front sight might be what you want.
The best competition rear sights are the Soules from MVA, Baldwin, and a few other US makers. The Pedersoli's are a little crude. The earlier style sights with simple vernier windage adjustment are harder to use, but more accurate to the buffalo harvest period. I don't think the Soule came along until the mid to late 1880's.
Most parctical hunting tang sight is probably a Marble's.
Hope this helps,
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