To be honest I'm not 100% - any info I have been able to find suggests that Mk1s had 8" drums, and Mk2s 9" drums, but I'm certainly happy to have someone confirm otherwise!
I didn't measure them when they were off the van, as I didn't do the work. But if I get bored I'm going to take them off or check for stampings to try and nail down exactly what they are.