For fitting the shock, just orient it so there is no binding. You might shim to keep it oriented correctly but that's a secondary issue.
Page 7 of the S2 workshop manual explains the general hardware part number scheme.
XUFB0602 is hex (X), fine thread (UF), bolt (B), 3/8" (2 digits 06 x 1/16 diameter), 1/8" (2 digiti 02 x 1/16 length). I think this is an error and should be XUFB0620 which would mean it's 1 1/4" long. I never worried about the bolt part number. I used AN bolts wherever I could so I had to measure all the grip length for pretty much each of them. You can measure the grip length and add enough for washers and the nut if needed.