Lazarus gun project build- inline or sidelock?

[Flophound]

It's long been a goal of mine to build my own gun from gathered parts cobbled together. I recently purchased a number of old barreled receivers of some 19th century bolt actions. French Gras and 1871 Mausers and Gewehr 18888s.
It seems to me that the simplest course of action would be to put in a breech plug and find a suitable bolt and bingo-bango it's an inline. There is the issue of these not being straight-walled chambers so the breech plug would need to be removable for proper cleaning. Or it just need to be about the length of the cartridge to its neck, say 1.5".
The other option as I see it would be to make it a sidelock. However, that would require butchering the action, which I'd rather not do- my idea is to add on to give new life to these guns.
Any input is greatly appreciated. I can provide pics if that would help.

Cheers,
flop

[Nobade]

Pretty simple to bore out the chamber, sleeve it, and use a breech plug. You might want to take a look at how Arrowhead rifles is making their replacement breech plugs for the Remington 700UML, that's how I would proceed if I wanted such a thing. Keep in mind you're going to also need a custom mould, likely paper patched to work in those barrels that are designed for long bullets.