Early speedos are 120mph, late are 140mph. Otherwise they are similar. See:
http://www.sccoa.com/forums/showthr...sale-89-93-and-2-94-95-sc&highlight=93+speedo
It's common with our speedos to have issues with a pair of small plastic gears inside the head.
Visit Bill Evanoff's site
https://www.supercoupeperformance.com/odometer-repair-kit-493 - to buy a repair kit. Note this thread from Bill about Black Fridays sales:
http://www.sccoa.com/forums/showthr...erformance-BLACK-FRIDAY-CYBER-MONDAY-SPECIALS
If you shop for an entire replacement speedo, I wouldn't bother with one that hasn't already had the gears replaced...might as well just rebuild yours. If that doesn't seem like something you'd want to tackle on your own, you might ask Bill about doing it for you, or, get the new gears and have a local speedo shop take a run at it. If you want to DIY, search here for discussion that might help you out. You need to open the dash and pull the speedo either way, tho. I had to replace the gears in mine last month. Not a bad job if you don't mind fragile puzzles