P3FE:
You don't say that you want an off the shelf factory built rifle, but I'm guessing that's what you mean.
I've had a slew of Thompson Centers, .50's and .54's in Renegade, White Mountain Carbine, Tree Hawk Carbine, Grey Hawk Carbine, one .32 Cherokee, everyone a capper, no flinters.
I still have I think 4 T/C rifles.
They have the BEST warranty in the business, great locks, very good triggers, good wood, nice fit and finish.
BUY THE LYMAN GREAT PLAINS RIFLE!!!!!!!!!!!!
Why??
All the T/C rifles I own, all .50's wear Green Mountain barrels, both roundball and fast twist bullet shooters.
Good thing T/C has the best warranty in the business because I know I've sent at least 6 or more back in the past 30 years.
I have NEVER, not once had a T/C Barrel in the 1:48 twist that shot anything, r/b or sabots, or bullets really well at 100 yards. That's from the bench with sandbag rest.
Others claim stellar accuracy with the 1:48 twist, but accuracy is a relative term.
Some hit a pie plate at 75 yards and proclaim the rifle acurrate. If I have a rifle that would only do that well it would soon be a boat anchor or tomatoe stake, or head down the road to a new home.
The little White Mountain Carbine in .54 was a bullet shooting TACK DRIVER with it's 21" barrel, but it was 1:38 twist, not 1:48 and was made to shoot the big heavy Maxiball. (nice name for a bullet what?) Even so that particular rifle made the trip back to the factory. TWICE.
Seems T/C rifled them wrong and didn't even know it. The third barrel was 1:38 twist, oddly the .50's were (some of 'em) rifled 1:20??????????? Beats me.
The Gray Hawk 21" barrel in .54 was pure junk on the target range as was the .32 Cherokee with it's weird 1:20 twist.
The Tree Hawk I currently have (for sale) is a wonderful shooter with sabots or bullets, have not tried roundballs.
I have two Lymans, a GPR in .54 Flint, roundballer, and a GPH 1:32 twist .54 bullet shooter. Both wear Lyman peep sights, both shoot better than I can hold them.
Buy the Lyman, (well you did ask for advice hey), clean that awefull packing lube from the metal paying particular attention to the bore, clean up the stock a bit and you'll have a rifle that looks good 'nuff to be an original.
or go with the T/C for considerably more $$$$$$$$$$ and not as good in the accuracy department.