One option might be to check out Holts et al for a Perkes style actioned gun.
These were retailed by the lowly and the mighty but are almost invariably very well finished inside even if plain on the outside.
Benefits include interceptor sears on the Block Safety or Boss system, 3 pin bridles that very rarely develope cracks, anti-friction rollers on the main springs (instead of swivels) and very easy adaptation to ejector.
Well known retailers include C&H, Blanch, H&H (Dominion & early No 2's)but the lesser known 'Makers will probably be just as good inside and cost a whole lot less.
Only downside is the leg of mutton lock shape which I love but may be too dated for your project.
