Select seadoo pwc, year, model, then find them on the fiche. If your year or ski doesn't have it, just go to the 96XP. All 787's use the same length screws. Not trying to give you the run around, but I know they list the length.
They're metric, M8's, but I don't remember the pitch. I had some missing here and there on the GSX build, particularly since the starter had been removed. I purchased the longest length M8's (allen head) in stainless pretty cheap on ebay, pack of 10. I cut and die rethreaded them where as appropriate.