Sorry but I can't help with selling you a speedo but I thought I'd share my experiences with a speedo
I had a rough speedo of unknown spec that I had refurbished but I did not know enough to specify exactly the spec I wanted to end up with so it is not quite right for my bike but I have spent $$$$$
There seems to be more to it than just the number on the dial! The number I have found does not always mean the spec is correct
Things that vary between speedos are the bezel as the bezel is flanged for speedos that fit in rubbers used with cowls and angled if fitted to a bracket
Some dials have the zero at the bottom left others top right
The case I started with was zinc plated but the refurber painted it black but I'm not sure what was Standard finish for speedos inside cowls maybe they were not painted?
Another speedo option is a case with a slot so light comes out from the speedo light to light up the ammeter inside the cowl Im not sure what is correct spec for the cowled a10's regarding slots also the slot on mine appears to be on the wrong side to light the ammeter
Obviously the number if revs of the cable per mile yr speedo needs is important but can be adjusted by a refurb company to suit the bike the speedo is going on the sc3305 (later a10 than mine) i have says it is 1450 revs per mile and I suspect the sc608 might be the same?
The rpm needs to be adjusted for the mph as well as miles as the mechanisms are separate for speed and distance thats what I've been told anyway
I bought a spare sc3305 speedo needing refurb for $50 recently but i was lucky! I've seen working ones go for well over 300 nzd on auction sites in nz