Hi, you must show pictures of such a beautiful car!!
A friend is looking to get his interior from these guys - Home
. As he has not done so yet, we can't vouch for quality.
What is the condition of the current interior? If it looks like a tiger has ripped through it, what is the point of keeping it like that? I think this whole originality things is a bit over-blown - I mean, do you have the original tyres, spark plugs, rubbers? Why are they less important to originality? Are you hoping to touch the old leather and somehow connect with all the events that they have been through?
Sorry for being cynical, but if the seats are dried out and cracked and torn and not serviceable, then I see no value in keeping them. Take the covers off and store them if you must. Perhaps a more pertinent question is this - will a new interior clash with the patina of the rest of the car? If the paint and chrome is a little tired, then a brand new interior can make that look worse - so then you end up thinking about respraying and re-chroming. This is a significant step change in $ and look. So if you do have patina that you like, perhaps try to find some used seats of the same colour that are more in keeping with the condition of the rest of the car.
Regardless of whether you store the whole seats or just the covers, it would pay to do a good round of leather feeding before you remove them, and periodically during storage, otherwise they will dry out and deteriorate.
Ultimately though it is a family decision, and what is cherished by your family cannot be foretold by complete strangers on the web. Good luck!