I guess you could give it a try. I'm sure you could find a frizzen and a main spring that will, or could be made to fit, and work just fine.
Ketlands were for their time a well made lock., not the best, but far from the worst.
However, I've seen quite a few of them with loose/worn fitting tumbler axles where they fit through the lock plate, plus looseness where the tumbler fits through the bridle, so you have to wonder about the hardness of the metal, and how it would do with a lot of shooting.
So your old lock might work fine, at least for awhile, and then maybe wear out quickly. Given that the lock does have some collector value, wearing it out will only diminish that value.
So I guess you could either fix it up and use it, fix it up and just admire it, or sell it as is and buy a couple of new lock with the bucks!
John