Rear spring spacers for S197

[Fishtail]

Lowering springs lowered the rear too much, so I'd like to bring it up using spacers. I'm in Canada and can't find a retailer that has the Kelltrac ones in stock that ships to Canada (American Muscle is out of stock). I'd like to raise it approximately 5/16". Has anyone used any other type of spacer? It looks like a large washer with an ID of approximately 61mm and OD of around 81mm would work on the bottom. I didn't have the spring out when measuring though, so I'm not sure how tall the centre retaining lip is on the axle...so I don't know if a 5/16" spacer would allow the spring to slide out of place. Any input would be appreciated.