I think if looking to be historicaly accurate the first thing to do is choose a particular fusil froma specific time/place of manufacture within a decade or so that will give you the architecture,typical barel length and bore size options rear sights can be placed on most types without to much of a squabble about HC/PC, then the type of sigth will be needed to be made this also can be done after the first two mentioned traits are made, if one wants a smoothrifle that is another critter, with a heavier barrel, rifle architecture and traits such as cheek piece,bow in trigger guard, patchbox and of course rear sight and bore size some rifle traits wee omited in some smoothrifles, this is just a very Basic check list to get you to a point where you can look at some of the options that you would have if historical accuray is of value, if not or at a very limited level many other doors will open and it would be hard to make something that is "wrong"
others with much more gun background than I may chime in and give you further guidance on this topic, there are many here who have years of research and gun building under their belts of where ever they keep it,good luck on the project.