Im sure one of the covers will work. Just incase you didnt know there are 2 different covers used on the roadsters. 1970 and then the 1971-74 used a different one, They look the same but are different lengths. I would recommend getting a parts list off ebay for the SS5 and I have all the part numbers for the roadster 2's and other rupp bikes and could help you cross reference part numbers.
Did you end up buying that tank on ebay?