Thanks again Mark-sf. I just got back from hols and measured my drive belt using the method you suggested. It is 560mm long. I think your figure of 88mm must be for a different belt? But thanks for the link to Beoparts-shop – this is a really useful, as they also sell the drive belt for the carriage servo motor, which I need.
Martin – thanks for the reminder about the carriage screws. I think these are fully withdrawn but will check again!