Hello Ian and welcome. Not built a Congreve clock but have made the English Regulator, which keeps excellent time.
I don't think that worn machinery should be a problem, you just need to learn and compensate for it. And another thing, a lot of clockmaking is handwork and even the turning does no need to be that accurate, the main thing is that parts should fit fairly loose so that there is no friction.
I wish you all the best with your project and look forward to reading updates on progress.
If you find you need help and advice then this is the place to come.
Brian