Just measured , the ones I have a 95 mm long & 20mm wide with a 4mm centre hole. the hole doesn't go all the way through , its only to hold a locating pin on the spring assembly.
Thanks for the Halson info. Actually got a set myself I'm gradually restoring that had seized. One elastomer in those had shrunk and gone rock hard and the other a gooey mess so the size info is very useful! Cheers!
I think the Mach5s use the standard 19mm diameter MCUs as per the XVerts etc. so that should be no problem. I'd just need to know your weight in kg so I can tailor the elastomer rates for you.